Search This Blog

Friday, September 22, 2023

Food system

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Food_system

The term food system describes the interconnected systems and processes that influence nutrition, food, health, community development, and agriculture. A food system includes all processes and infrastructure involved in feeding a population: growing, harvesting, processing, packaging, transporting, marketing, consumption, distribution, and disposal of food and food-related items. It also includes the inputs needed and outputs generated at each of these steps. Food systems fall within agri-food systems, which encompass the entire range of actors and their interlinked value-adding activities in the primary production of food and non-food agricultural products, as well as in food storage, aggregation, post-harvest handling, transportation, processing, distribution, marketing, disposal, and consumption. A food system operates within and is influenced by social, political, economic, technological and environmental contexts. It also requires human resources that provide labor, research and education. Food systems are either conventional or alternative according to their model of food lifespan from origin to plate. Food systems are dependent on a multitude of ecosystem services. For example, natural pest regulations, microorganisms providing nitrogen-fixation, and pollinators. 

According to the IPCC, the global food system, including all of the various industries involved in sustainable and conventional food systems, provide employment for 1 billion people. This global food system is facing a number of challenges created by impeding global food security issues created by climate change and non-climate change stresses on the system. About 34% of total greenhouse gas emissions are attributable to the global food system. In 2020 an EU evidence review found that food system gas emissions are on course to increase by 30–40% by 2050 due to population growth and dietary change. According to FAO, it is crucial to build the resilience of agrifood systems so that they have the capacity over time, in the face of any disruption, to sustainably ensure availability of and access to sufficient, safe and nutritious food for all, and sustain the livelihoods of agrifood systems' actors.

Transitioning to sustainable food systems is critical for addressing global challenges such as climate change, hunger, biodiversity loss, and deforestation. Addressing issues at each stage in the system, can have system-wide effects for 30-40 percent of food produced is lost from post-harvest up to retail and the consumer. Reducing food waste then reduces the environmental impacts of agriculture, such as land use impacts, and reducing food prices or preventing shortages. International policy has increasingly approached policy from a food systems perspective: Sustainable Development Goal 2: Zero Hunger and Sustainable Development Goal 12: "responsible consumption and production" focus on sustainable food systems and Sustainable and in September 2021 the United Nations hosted the first Food Systems Summit.

Conventional food systems

Conventional food systems operate on economies of scale. These food systems are geared towards a production model that requires maximizing efficiency in order to lower consumer costs and increase overall production, and they utilize economic models such as vertical integration, economic specialization, and global trade. The growing soil quality degradation, climate change, and growing world population put pressure on agricultural land, leading to innovations to increase agricultural productivity on the limited available land and urban space. Though conventional farming practices have increased crop yield through the use of climate-smart agriculture (CSA), smallholder farming systems and limited knowledge of CSA remain constraints for enjoying economies of scale and sustainable crop production and food security.

The term “conventional” when describing food systems is largely due to comparisons made to it by proponents of other food systems, collectively known as alternative food systems.

History of conventional food systems

The development of food systems can be traced back to the origins of in-situ agriculture and the production of food surpluses. These surpluses enabled the development of settled areas and contributed to the development of ancient civilizations, particularly those in the Fertile Crescent. The system of trade associated with the exchange of foodstuffs also emerged in East Asia, North America, South America, and Subsaharan Africa with common commodities of exchange such as salt, spices, fish, grains, etc. Through events in world history such as the conquests of Alexander the Great, the Crusades, the expansion of Islam, the journeys of Marco Polo, and the exploration and colonization of the Americas by Europeans led to the introduction and redistribution of new foods to the world at large, and food systems began to intermingle on a global scale. After World War II, the advent of industrialized agriculture and more robust global trade mechanisms have evolved into the models of food production, presentation, delivery, and disposal that characterize conventional food systems today.

Impacts of conventional food systems

The development of conventional food systems is directly responsible for decreased food prices and increased food variety. Agronomic efficiency is driven by the necessity to constantly lower production expenses, and those savings can then be passed on to the consumer. Also, the advent of industrial agriculture and the infrastructure built around conventional food systems has enabled the world population to expand beyond the "Malthusian catastrophe" limitations. According to the IPCC, food supply per capita has increased by more than 30% since 1961.

However, conventional food systems are largely based on the availability of inexpensive fossil fuels, which is necessary for mechanized agriculture, the manufacture or collection of chemical fertilizers, the processing of food products, and the packaging of the foods. The increase in the availability of food since 1961 has primarily been driven by an 800% increase in the use of nitrogen fertilizers (which are fossil fuel dependent) and high water usage (an increase of over 100% since 1961).

The impacts of these intense resource processes are many a varied: food processing began when the number of consumers started proliferating. The demand for cheap and efficient calories climbed, resulting in nutrition decline; and industrialized agriculture, due to its reliance on economies of scale to reduce production costs, often leads to the compromising of local, regional, or even global ecosystems through fertilizer runoff, nonpoint source pollution, and greenhouse gas emission.

The need to reduce production costs in an increasingly global market can cause the production of foods to be moved to areas where economic costs (labor, taxes, etc.) are lower or environmental regulations are laxer, which are usually further from consumer markets. For example, the majority of salmon sold in the United States is raised off the coast of Chile, due in large part to less stringent Chilean standards regarding fish feed and regardless of the fact that salmon are not indigenous in Chilean coastal waters. The globalization of food production can result in the loss of traditional food systems in less developed countries, and have negative impacts on the population health, ecosystems, and cultures in those countries. As a result of these forces, 2018 estimates suggest that 821 million people are currently undernourished, and 2 billion adults are overweight and obese.

The issue of having minimal access to food, or access to primarily unhealthy food, is often described in terms of food security. The 1996 World Food Summit defined food security as a state in which "all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life. " Many groups argue that food security is largely determined by a given person's socioeconomic status, race, ethnicity, or other socially defined categories, making food access a social justice issue. This has given rise to numerous social movements whose goal is to increase access to healthy and culturally appropriate foods, among a wide variety of groups. These movements are often described as belonging to a more significant food justice movement.

Scientists estimated the extensive pesticide pollution risks worldwide with a new environmental model and found that a third of global agricultural land is at high risk for such pollution, of which a third are high-biodiversity regions.

Sustainable food systems

A sustainable food system is a type of food system that provides healthy food to people and creates sustainable environmental, economic, and social systems that surround food. Sustainable food systems start with the development of sustainable agricultural practices, development of more sustainable food distribution systems, creation of sustainable diets, and reduction of food waste throughout the system. Sustainable food systems have been argued to be central to many or all 17 Sustainable Development Goals.

Moving to sustainable food systems, including via shifting consumption to sustainable diets, is an important component of addressing the causes of climate change and adapting to it. A 2020 review conducted for the European Union found that up to 37% of global greenhouse gas emissions could be attributed to the food system, including crop and livestock production, transportation, changing land use (including deforestation), and food loss and waste. Reduction of meat production, which accounts for ~60% of greenhouse gas emissions and ~75% of agriculturally used land, is one major component of this change.

The global food system is facing major interconnected challenges, including mitigating food insecurity, effects from climate change, biodiversity loss, malnutrition, inequity, soil degradation, pest outbreaks, water and energy scarcity, economic and political crises, natural resource depletion, and preventable ill-health.

The concept of sustainable food systems is frequently at the center of sustainability-focused policy programs, such as proposed Green New Deal programs.

Local food systems

A map of wheat production (average percentage of land used for its production times average yield in each grid cell) across the world.

Local food systems are networks of food production and consumption that aim to be geographically and economically accessible and direct. They contrast to industrial food systems by operating with reduced food transportation and more direct marketing, leading to fewer people between the farmer and the consumer. As a result, relationships that are developed in local food systems emerge from face-to-face interactions, potentially leading to a stronger sense of trust and social connectedness between actors. In addition to this, consumers can also encourage farmers to be environmentally friendly by teaching them about practices such as organic farming. As a result, some scholars suggest that local food systems are a good way to revitalize a community. The decreased distance of food transportation has also been promoted for its environmental benefits. Also, farmers can enjoy a better quality of life because producing healthier food will allow them to be paid more, and not live under the poverty line.

Both proponents and critics of local food systems warn that they can lead to narrow inward-looking attitudes or ‘local food patriotism’, and that price premiums and local food cultures can be elitist and exclusive. In contrast, many food sovereignty activists argue that local production of food is essential to achieving food security, especially among indigenous communities, and thus are crucial to the public health of those communities.

Examples of local food systems include community-supported agriculture, farmers markets and farm to school programs. They have been associated with the 100 Mile Diet and Low Carbon Diet, as well as the slow food movement. The food sovereignty movement is also related to local food production. Food sovereignty activists argue that local communities should not only have access to nutritious and culturally appropriate foods, but that those communities should also be able to define the means by which their food is produced. Various forms of urban agriculture locate food production in densely populated areas not traditionally associated with farming. Garden sharing, where urban and suburban homeowners offer land access to food growers in exchange for a share of the harvest, is a relatively new trend, at the extreme end of direct local food production.

An FAO study on food transport networks of 90 countries finds that where food is transported more locally and where the network is denser – such as in high-income countries and densely populated countries like China, India, Nigeria and Pakistan –, systematic disturbances (i.e., adverse events), have a much lower impact on increases in travel time and food costs than where food is transported further distances.

Organic food systems

An organic certification

Organic food systems are characterized by a reduced dependence on chemical inputs and an increased concern for transparency and information. Organic produce is grown without the chemical pesticides and fertilizers of industrial food systems, and livestock is reared without the use of antibiotics or growth hormones. The reduced inputs of organic agriculture can also lead to a greater reliance on local knowledge, creating a stronger knowledge community amongst farmers. The transparency of food information is vital for organic food systems as a means through which consumers are able to identify organic food. As a result, a variety of certification bodies have emerged in organic food systems that set the standards for organic identification. Organic agriculture is promoted for the ecological benefits of reduced chemical application, the health benefits of lower chemical consumption, the economic benefits that accrue to farmers through a price premium, and the social benefits of increased transparency in the food system.

Organic food systems have been criticized for being elitist and inaccessible like local food systems. Critics have also suggested that organic agriculture has been conventionalized such that it mimics industrial food systems using pesticides and fertilizers that are organically derived.

Cooperatives in food systems

A greenhouse with salad of a cooperative
An organic food box of a organic food delivery service
A farmers' market offering food produced by community-supported agriculture that is also delivering online orders

Cooperatives can exist both at the farmer end of food production and the consumer end. Farming cooperatives refer to arrangements where farmers pool resources, either to cultivate their crops or get their crops to market. Consumer cooperatives often refer to food cooperatives where members buy a share in the store. Cooperative grocery stores, unlike corporate grocery stores, are socially owned, and thus surpluses cannot be taken from the store as profit. As a result, food co-ops do not work for profit, potentially keeping prices more cost representative. Other forms of cooperatives that have developed more recently include community-supported agriculture, where community members buy a share in a farm's harvest, and may also be engaged in farm labor, operating at both the consumer and producer end of food systems. Garden sharing pairs individual landowners and food growers, while variations on this approach organize groups of food gardeners for mutual assistance.

Producer associations and cooperatives reinforce small-scale agricultural producers’ livelihoods by allowing the pooling of resources to achieve scale, facilitating access to productive resources, and enhancing  marketing power. Coordination with other actors is also key to managing market risks. Mutual benefits can be achieved, for example, through forwarding contracts: farmers receive guaranteed prices for their outputs regardless of market conditions, while processors and distributors receive products of a desired quality. For farming cooperatives that share resources, the burden of investment is disbursed to all members rather than being concentrated in a single individual. A criticism of cooperatives is that reduced competition can reduce efficiency.

Alternative food systems

Alternative food systems refer to resilient foods or emergency foods, which can be defined as those foods, food production methods or interventions that would allow for significant food availability in the face of a global catastrophic food shock (GCFS). An expected 345.2 million people projected to be food insecure in 2023 – more than double the number in 2020, but a global catastrophe such as nuclear winter could threaten billions with mass starvation. Several studies have argued resilient food could provide the calories to support the global population even without agriculture. According to the book Feeding Everyone No Matter What and peer-reviewed study paths to a full solution include: global-scale conversion including natural gas-digesting bacteria (single cell protein), extracting food from leaves, and conversion of fiber by enzymes, mushroom or bacteria growth, or a two-step process involving partial decomposition of fiber by fungi and/or bacteria and feeding them to animals such as beetles, ruminants (cattle, sheep, etc.), rats and chickens. Most alternative food work covers carbohydrates and protein, but there are also ways to make synthetic fat. By mixing many alternative foods micro-nutrient balance is possible. Substantially more research is needed in this area to realize resilient food systems for the globe and even wealthy nations.

Fair trade

Fair trade may require decisions that lead to relevant supply-chain management.

Fair trade has emerged in global food systems to create a more excellent balance between food price and the cost of producing it. It is mainly defined by more direct trading and communication systems whereby producers have greater control over the conditions of trade and garner a greater fraction of the sale price. The main goal of Fair Trade is to "change international commercial relations in such a way that disadvantaged producers can increase their control over their own future, have a fair and just return for their work, continuity of income and decent working and living conditions through sustainable development"  Like organic food systems, fair trade relies on transparency and the flow of information. Well-known examples of fair trade commodities are coffee and cocoa.

Climate change

Effects of climate change

The IPCC Special Report on Climate Change and Land describes the current global food system as potentially having major food security risks due to changes created by climate change, including changing local weather conditions, socioeconomic effects of climate change, vulnerability of certain types of agriculture (such as pastoral) and changes in diets due to availability.

Effects on climate change

The heavy industrialization of USA, Europe and China is responsible for 90% of the world's pollution.
Deforestation in Indonesia is mainly driven by nonintervention in processes related to the production and consumption of palm oil and has a large impact on climate change.
Deforestation in Europe, 2020. The continent reduced its original vegetation cover to less than 30% in order to carry out its agriculture and livestock.

The food system is one of the largest sources of greenhouse gas emissions, attributable for between 21 and 37% of global emissions. In 2020, an evidence review for the European Union's Scientific Advice Mechanism found that, without significant change, emissions would increase by 30–40% by 2050 due to population growth and changing consumption patterns, and concluded that "the combined environmental cost of food production is estimated to amount to some $12 trillion per year, increasing to $16 trillion by 2050". Another 2020 study concluded that reducing emissions from the global food system to be essential for achieving the Paris Agreement's climate goals.

The IPCC's and the EU's reports concluded that adapting the food system to reduce greenhouse gas emissions impacts and food security concerns, while shifting towards a sustainable diet, is feasible.

Public policy

European Union

The European Union's Scientific Advice Mechanism has published a systematic review of all European policies related to sustainable food systems, and their analyses in the academic literature.

In September 2019, the EU's Chief Scientific Advisors stated that adapting the European food system for the future should be a high priority for the EU:

Although availability of food is not perceived as an immediate, major concern in Europe, the challenge to ensure a long-term, safe, nutritious and affordable supply of food, from both land and the oceans, remains. A portfolio of coordinated strategies is called for to address this challenge.

In January 2020, the EU put improvements to the food system at the core of the European Green Deal. The European Commission's 'Farm to Fork strategy for a sustainable food system' was published in May 2020, which laid out how European countries will reduce greenhouse gas emissions, protect biodiversity, reduce food waste and chemical pesticide use, and contribute to a circular economy.

In April 2020, the EU's Scientific Advice Mechanism delivered to European Commissioners a Scientific Opinion on how to transition to a sustainable food system, informed by an evidence review report undertaken by European academies.

In June 2023, the Scientific Advice Mechanism delivered a second piece of advice, this time on the role of consumers in a sustainable food system, again based on an evidence review report by SAPEA. The main conclusion of this advice was:

Until now, the main policy focus in the EU has been on providing consumers with more information. But this is not enough. People choose food not just through rational reflection, but also based on many other factors: food availability, habits and routines, emotional and impulsive reactions, and their financial and social situation. So we should consider ways to unburden the consumer and make sustainable, healthy food an easy and affordable choice. That will require a mix of incentives, information and binding policies governing all aspects of food production and distribution.

Public–Private Partnerships

Private sector corporations have been successful in building partnerships with governments which allows discussion and collaboration for how food systems work and are governed. Public–private partnerships and private sector led multistakeholder governance have positioned corporations as a leading voice on decisions where public governance authorities have become dependent on private sector funding. Lobbying influences trade agreements for food systems which led to creating barriers to competition and technical barriers to trade. Concerns around corporate governance within food systems as a substitute for regulation were raised by the Institute for Multi-Stakeholder Initiative Integrity. In April 2023, United States Agency for International Development (USAID) and the Global Food Safety Initiative (GFSI) announced a Memorandum of Understanding (MOU) to improve food safety and sustainable food systems in Africa.

Transparency

Transparency within food systems refers to the full disclosure of information about rules, procedures, and practices at all levels within a food production and supply chain. Transparency ensures that consumers have detailed information about the production of a given food item. Traceability, by contrast, is the ability to trace to their origins all components in a food production and marketing chain, whether processed or unprocessed (e.g., meat, vegetables) foods. Concerns about transparency and traceability have been heightened with food safety scares such as bovine spongiform encephalopathy (BSE) and Escherichia coli (E. coli), but do not exclusively refer to food safety. Transparency is also important in identifying foods that possess extrinsic qualities that do not affect the nature of the food per se, but affect its production, such as animal welfare, social justice issues, and environmental concerns.

One of the primary ways transparency is achieved is through certification and/or the use of food labels. In the United States, some certification originates in the public sector, such as the United States Department of Agriculture (USDA) Organic label. Others have their origin in private sector certification (e.g., Humanely Raised, Certified Humane). Some labels do not rely on certification, such as the USDA's Country of Origin Label (COOL).

Participation in local food systems such as Community Supported Agriculture (CSA), Farmers Markets, food cooperatives, and farmer cooperatives also enhances transparency. Diverse program are promoting purchase of locally grown and marketed foods.

In June 2023, the Scientific Advice Mechanism to the European Commission concluded that "Evidence generally supports a moderate impact of nutrition labelling on (un)healthy consumption in different contexts (retail, out-of-home). Sustainability-oriented labels tend to reach those who are already motivated and interested, and they strongly depend on the trustworthiness of labels, given that sustainability cannot be directly observed by consumers. However, there is much less research devoted to sustainability labelling in comparison to nutritional labelling. To conclude, shaping the information environment through labelling is necessary but not sufficient to advance healthy and sustainable diets".

Labeling

USDA Organic Label
Organic (USA) – The USDA Organic label indicates that the product has been produced in accordance with the USDA's Federal Organic Standard, part of the National Organic Program federal regulatory framework. This label is applied to fruits, vegetables, meat, eggs and dairy products. Some states, such as California, have their own organic label. Organic labelling is prominent internationally as well.
Fair Trade Show in UK
Fair Trade – Indicates that the product has been grown and marketed in accordance with Fair Trade standards. This is an independent certification, awarded by FLO-CERT and overseen by FLO International. Major food items that are marketed under Fair Trade are coffee, tea and chocolate. Many items other than food are sold with a Fair Trade label.

Food Alliance Certified – Food Alliance is a nonprofit organization that certifies farms, ranches, and food processors and distributors for safe and fair working conditions, humane treatment of animals, and good environmental stewardship. Food Alliance Certified products come from farms, ranches and food processors that have met meaningful standards for social and environmental responsibility, as determined through an independent third-party audit. Food Alliance does not certify genetically modified crops or livestock. Meat or dairy products come from animals that are not treated with antibiotics or growth hormones. Food Alliance Certified foods never contain artificial colors, flavors, or preservatives.
Examples of COOL Labeling
Country of Origin – This label was created by enactment of the 2002 Farm Bill. The US Department of Agriculture is responsible for its implementation, which began 30 September 2008. The bill mandates country of origin labeling for several products, including beef, lamb, pork, fish, chicken, perishable agricultural commodities and some nuts. USDA rules provide specifics as to documentation, timetables and definitions. There is not one specific label to indicate the country of origin; they will vary by country.

American Humane Certified – This certification is provided by the American Humane Association, and ensures that farm animals are raised according to welfare standards that provide for adequate housing, feed, healthcare and behavior expression. Antibiotics are not used except for therapeutic reasons; growth promoters are not used. Other issues including transport, processing and biosecurity are addressed as well. Species covered are poultry, cattle and swine.

Certified Humane Raised & Handled – This label ensures that production meets the Humane Farm Animal Care Program standards, which addresses housing, diet (excluding routine use of hormones or antibiotics) and natural behavior. Additionally, producers must comply with food safety and environmental protection regulations. They must meet standards set by the American Meat Institute, that are more stringent than those laid out in the Federal Humane Slaughter Act. Certification has been applied to beef, poultry and eggs, pork, lamb, goat, turkey, veal, dairy products and wool.

 

Visual search

From Wikipedia, the free encyclopedia

Visual search is a type of perceptual task requiring attention that typically involves an active scan of the visual environment for a particular object or feature (the target) among other objects or features (the distractors). Visual search can take place with or without eye movements. The ability to consciously locate an object or target amongst a complex array of stimuli has been extensively studied over the past 40 years. Practical examples of using visual search can be seen in everyday life, such as when one is picking out a product on a supermarket shelf, when animals are searching for food among piles of leaves, when trying to find a friend in a large crowd of people, or simply when playing visual search games such as Where's Wally?

Much previous literature on visual search used reaction time in order to measure the time it takes to detect the target amongst its distractors. An example of this could be a green square (the target) amongst a set of red circles (the distractors). However, reaction time measurements do not always distinguish between the role of attention and other factors: a long reaction time might be the result of difficulty directing attention to the target, or slowed decision-making processes or slowed motor responses after attention is already directed to the target and the target has already been detected. Many visual search paradigms have therefore used eye movement as a means to measure the degree of attention given to stimuli. However, eyes can move independently of attention, and therefore eye movement measures do not completely capture the role of attention.

Search types

Feature search

feature based search task

Feature search (also known as "disjunctive" or "efficient" search) is a visual search process that focuses on identifying a previously requested target amongst distractors that differ from the target by a unique visual feature such as color, shape, orientation, or size. An example of a feature search task is asking a participant to identify a white square (target) surrounded by black squares (distractors). In this type of visual search, the distractors are characterized by the same visual features. The efficiency of feature search in regards to reaction time(RT) and accuracy depends on the "pop out" effect, bottom-up processing, and parallel processing. However, the efficiency of feature search is unaffected by the number of distractors present.

The "pop out" effect is an element of feature search that characterizes the target's ability to stand out from surrounding distractors due to its unique feature. Bottom-up processing, which is the processing of information that depends on input from the environment, explains how one utilizes feature detectors to process characteristics of the stimuli and differentiate a target from its distractors. This draw of visual attention towards the target due to bottom-up processes is known as "saliency." Lastly, parallel processing is the mechanism that then allows one's feature detectors to work simultaneously in identifying the target.

Conjunction search

Conjunctive based search task.

Conjunction search (also known as inefficient or serial search) is a visual search process that focuses on identifying a previously requested target surrounded by distractors possessing no distinct features from the target itself. An example of a conjunction search task is having a person identify a red X (target) amongst distractors composed of black Xs (same shape) and red Os (same color). Unlike feature search, conjunction search involves distractors (or groups of distractors) that may differ from each other but exhibit at least one common feature with the target. The efficiency of conjunction search in regards to reaction time(RT) and accuracy is dependent on the distractor-ratio and the number of distractors present. As the distractors represent the differing individual features of the target more equally amongst themselves(distractor-ratio effect), reaction time(RT) increases and accuracy decreases. As the number of distractors present increases, the reaction time(RT) increases and the accuracy decreases. However, with practice the original reaction time(RT) restraints of conjunction search tend to show improvement. In the early stages of processing, conjunction search utilizes bottom-up processes to identify pre-specified features amongst the stimuli. These processes are then overtaken by a more serial process of consciously evaluating the indicated features of the stimuli in order to properly allocate one's focal spatial attention towards the stimulus that most accurately represents the target.

In many cases, top-down processing affects conjunction search by eliminating stimuli that are incongruent with one's previous knowledge of the target-description, which in the end allows for more efficient identification of the target. An example of the effect of top-down processes on a conjunction search task is when searching for a red 'K' among red 'Cs' and black 'Ks', individuals ignore the black letters and focus on the remaining red letters in order to decrease the set size of possible targets and, therefore, more efficiently identify their target.

Real world visual search

In everyday situations, people are most commonly searching their visual fields for targets that are familiar to them. When it comes to searching for familiar stimuli, top-down processing allows one to more efficiently identify targets with greater complexity than can be represented in a feature or conjunction search task. In a study done to analyze the reverse-letter effect, which is the idea that identifying the asymmetric letter among symmetric letters is more efficient than its reciprocal, researchers concluded that individuals more efficiently recognize an asymmetric letter among symmetric letters due to top-down processes. Top-down processes allowed study participants to access prior knowledge regarding shape recognition of the letter N and quickly eliminate the stimuli that matched their knowledge. In the real world, one must use prior knowledge everyday in order to accurately and efficiently locate objects such as phones, keys, etc. among a much more complex array of distractors. Despite this complexity, visual search with complex objects (and search for categories of objects, such as "phone", based on prior knowledge) appears to rely on the same active scanning processes as conjunction search with less complex, contrived laboratory stimuli, although global statistical information available in real-world scenes can also help people locate target objects. While bottom-up processes may come into play when identifying objects that are not as familiar to a person, overall top-down processing highly influences visual searches that occur in everyday life. Familiarity can play especially critical roles when parts of objects are not visible (as when objects are partly hidden from view because they are behind other objects). Visual information from hidden parts can be recalled from long-term memory and used to facilitate search for familiar objects.

Reaction time slope

It is also possible to measure the role of attention within visual search experiments by calculating the slope of reaction time over the number of distractors present. Generally, when high levels of attention are required when looking at a complex array of stimuli (conjunction search), the slope increases as reaction times increase. For simple visual search tasks (feature search), the slope decreases due to reaction times being fast and requiring less attention. However, the use of a reaction time slope to measure attention is controversial because non-attentional factors can also affect reaction time slope.

Visual orienting and attention

A photograph that simulates foveation

One obvious way to select visual information is to turn towards it, also known as visual orienting. This may be a movement of the head and/or eyes towards the visual stimulus, called a saccade. Through a process called foveation, the eyes fixate on the object of interest, making the image of the visual stimulus fall on the fovea of the eye, the central part of the retina with the sharpest visual acuity.

There are two types of orienting:

  • Exogenous orienting is the involuntary and automatic movement that occurs to direct one's visual attention toward a sudden disruption in his peripheral vision field. Attention is therefore externally guided by a stimulus, resulting in a reflexive saccade.
  • Endogenous orienting is the voluntary movement that occurs in order for one to focus visual attention on a goal-driven stimulus. Thus, the focus of attention of the perceiver can be manipulated by the demands of a task. A scanning saccade is triggered endogenously for the purpose of exploring the visual environment.
A plot of the saccades made while reading text. The plot shows the path of eye movements and the size of the circles represents the time spent at any one location.

Visual search relies primarily on endogenous orienting because participants have the goal to detect the presence or absence of a specific target object in an array of other distracting objects.

Early research suggested that attention could be covertly (without eye movement) shifted to peripheral stimuli, but later studies found that small saccades (microsaccades) occur during these tasks, and that these eye movements are frequently directed towards the attended locations (whether or not there are visible stimuli). These findings indicate that attention plays a critical role in understanding visual search.

Subsequently, competing theories of attention have come to dominate visual search discourse. The environment contains a vast amount of information. We are limited in the amount of information we are able to process at any one time, so it is therefore necessary that we have mechanisms by which extraneous stimuli can be filtered and only relevant information attended to. In the study of attention, psychologists distinguish between pre-attentive and attentional processes. Pre-attentive processes are evenly distributed across all input signals, forming a kind of "low-level" attention. Attentional processes are more selective and can only be applied to specific preattentive input. A large part of the current debate in visual search theory centres on selective attention and what the visual system is capable of achieving without focal attention.

Theory

Feature integration theory (FIT)

A popular explanation for the different reaction times of feature and conjunction searches is the feature integration theory (FIT), introduced by Treisman and Gelade in 1980. This theory proposes that certain visual features are registered early, automatically, and are coded rapidly in parallel across the visual field using pre-attentive processes. Experiments show that these features include luminance, colour, orientation, motion direction, and velocity, as well as some simple aspects of form. For example, a red X can be quickly found among any number of black Xs and Os because the red X has the discriminative feature of colour and will "pop out." In contrast, this theory also suggests that in order to integrate two or more visual features belonging to the same object, a later process involving integration of information from different brain areas is needed and is coded serially using focal attention. For example, when locating an orange square among blue squares and orange triangles, neither the colour feature "orange" nor the shape feature "square" is sufficient to locate the search target. Instead, one must integrate information of both colour and shape to locate the target.

Evidence that attention and thus later visual processing is needed to integrate two or more features of the same object is shown by the occurrence of illusory conjunctions, or when features do not combine correctly For example, if a display of a green X and a red O are flashed on a screen so briefly that the later visual process of a serial search with focal attention cannot occur, the observer may report seeing a red X and a green O.

The FIT is a dichotomy because of the distinction between its two stages: the preattentive and attentive stages. Preattentive processes are those performed in the first stage of the FIT model, in which the simplest features of the object are being analyzed, such as color, size, and arrangement. The second attentive stage of the model incorporates cross-dimensional processing, and the actual identification of an object is done and information about the target object is put together. This theory has not always been what it is today; there have been disagreements and problems with its proposals that have allowed the theory to be amended and altered over time, and this criticism and revision has allowed it to become more accurate in its description of visual search. There have been disagreements over whether or not there is a clear distinction between feature detection and other searches that use a master map accounting for multiple dimensions in order to search for an object. Some psychologists support the idea that feature integration is completely separate from this type of master map search, whereas many others have decided that feature integration incorporates this use of a master map in order to locate an object in multiple dimensions.

The FIT also explains that there is a distinction between the brain's processes that are being used in a parallel versus a focal attention task. Chan and Hayward have conducted multiple experiments supporting this idea by demonstrating the role of dimensions in visual search. While exploring whether or not focal attention can reduce the costs caused by dimension-switching in visual search, they explained that the results collected supported the mechanisms of the feature integration theory in comparison to other search-based approaches. They discovered that single dimensions allow for a much more efficient search regardless of the size of the area being searched, but once more dimensions are added it is much more difficult to efficiently search, and the bigger the area being searched the longer it takes for one to find the target.

Guided search model

A second main function of preattentive processes is to direct focal attention to the most "promising" information in the visual field. There are two ways in which these processes can be used to direct attention: bottom-up activation (which is stimulus-driven) and top-down activation (which is user-driven). In the guided search model by Jeremy Wolfe, information from top-down and bottom-up processing of the stimulus is used to create a ranking of items in order of their attentional priority. In a visual search, attention will be directed to the item with the highest priority. If that item is rejected, then attention will move on to the next item and the next, and so forth. The guided search theory follows that of parallel search processing.

An activation map is a representation of visual space in which the level of activation at a location reflects the likelihood that the location contains a target. This likelihood is based on preattentive, featural information of the perceiver. According to the guided search model, the initial processing of basic features produces an activation map, with every item in the visual display having its own level of activation. Attention is demanded based on peaks of activation in the activation map in a search for the target. Visual search can proceed efficiently or inefficiently. During efficient search, performance is unaffected by the number of distractor items. The reaction time functions are flat, and the search is assumed to be a parallel search. Thus, in the guided search model, a search is efficient if the target generates the highest, or one of the highest activation peaks. For example, suppose someone is searching for red, horizontal targets. Feature processing would activate all red objects and all horizontal objects. Attention is then directed to items depending on their level of activation, starting with those most activated. This explains why search times are longer when distractors share one or more features with the target stimuli. In contrast, during inefficient search, the reaction time to identify the target increases linearly with the number of distractor items present. According to the guided search model, this is because the peak generated by the target is not one of the highest.

Biological basis

A pseudo-color image showing activation of the primary visual cortex during a perceptual task using functional magnetic resonance imaging (fMRI)

During visual search experiments the posterior parietal cortex has elicited much activation during functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) experiments for inefficient conjunction search, which has also been confirmed through lesion studies. Patients with lesions to the posterior parietal cortex show low accuracy and very slow reaction times during a conjunction search task but have intact feature search remaining to the ipsilesional (the same side of the body as the lesion) side of space. Ashbridge, Walsh, and Cowey in (1997) demonstrated that during the application of transcranial magnetic stimulation (TMS) to the right parietal cortex, conjunction search was impaired by 100 milliseconds after stimulus onset. This was not found during feature search. Nobre, Coull, Walsh and Frith (2003) identified using functional magnetic resonance imaging (fMRI) that the intraparietal sulcus located in the superior parietal cortex was activated specifically to feature search and the binding of individual perceptual features as opposed to conjunction search. Conversely, the authors further identify that for conjunction search, the superior parietal lobe and the right angular gyrus elicit bilaterally during fMRI experiments.

Visual search primarily activates areas of the parietal lobe.

In contrast, Leonards, Sunaert, Vam Hecke and Orban (2000) identified that significant activation is seen during fMRI experiments in the superior frontal sulcus primarily for conjunction search. This research hypothesises that activation in this region may in fact reflect working memory for holding and maintaining stimulus information in mind in order to identify the target. Furthermore, significant frontal activation including the ventrolateral prefrontal cortex bilaterally and the right dorsolateral prefrontal cortex were seen during positron emission tomography for attentional spatial representations during visual search. The same regions associated with spatial attention in the parietal cortex coincide with the regions associated with feature search. Furthermore, the frontal eye field (FEF) located bilaterally in the prefrontal cortex, plays a critical role in saccadic eye movements and the control of visual attention.

Moreover, research into monkeys and single cell recording found that the superior colliculus is involved in the selection of the target during visual search as well as the initiation of movements. Conversely, it also suggested that activation in the superior colliculus results from disengaging attention, ensuring that the next stimulus can be internally represented. The ability to directly attend to a particular stimuli during visual search experiments has been linked to the pulvinar nucleus (located in the midbrain) while inhibiting attention to unattended stimuli. Conversely, Bender and Butter (1987) found that during testing on monkeys, no involvement of the pulvinar nucleus was identified during visual search tasks.

There is evidence for the V1 Saliency Hypothesis that the primary visual cortex (V1) creates a bottom-up saliency map to guide attention exogenously, and this V1 saliency map is read out by the superior colliculus which receives monosynaptic inputs from V1.

Evolution

There is a variety of speculation about the origin and evolution of visual search in humans. It has been shown that during visual exploration of complex natural scenes, both humans and nonhuman primates make highly stereotyped eye movements. Furthermore, chimpanzees have demonstrated improved performance in visual searches for upright human or dog faces, suggesting that visual search (particularly where the target is a face) is not peculiar to humans and that it may be a primal trait. Research has suggested that effective visual search may have developed as a necessary skill for survival, where being adept at detecting threats and identifying food was essential.

Henri Rousseau, Jungle with Lion

The importance of evolutionarily relevant threat stimuli was demonstrated in a study by LoBue and DeLoache (2008) in which children (and adults) were able to detect snakes more rapidly than other targets amongst distractor stimuli. However, some researchers question whether evolutionarily relevant threat stimuli are detected automatically.

Face recognition

Over the past few decades there have been vast amounts of research into face recognition, specifying that faces endure specialized processing within a region called the fusiform face area (FFA) located in the mid fusiform gyrus in the temporal lobe. Debates are ongoing whether both faces and objects are detected and processed in different systems and whether both have category specific regions for recognition and identification. Much research to date focuses on the accuracy of the detection and the time taken to detect the face in a complex visual search array. When faces are displayed in isolation, upright faces are processed faster and more accurately than inverted faces, but this effect was observed in non-face objects as well. When faces are to be detected among inverted or jumbled faces, reaction times for intact and upright faces increase as the number of distractors within the array is increased. Hence, it is argued that the 'pop out' theory defined in feature search is not applicable in the recognition of faces in such visual search paradigm. Conversely, the opposite effect has been argued and within a natural environmental scene, the 'pop out' effect of the face is significantly shown. This could be due to evolutionary developments as the need to be able to identify faces that appear threatening to the individual or group is deemed critical in the survival of the fittest. More recently, it was found that faces can be efficiently detected in a visual search paradigm, if the distracters are non-face objects, however it is debated whether this apparent 'pop out' effect is driven by a high-level mechanism or by low-level confounding features. Furthermore, patients with developmental prosopagnosia, who have impaired face identification, generally detect faces normally, suggesting that visual search for faces is facilitated by mechanisms other than the face-identification circuits of the fusiform face area.

Patients with forms of dementia can also have deficits in facial recognition and the ability to recognize human emotions in the face. In a meta-analysis of nineteen different studies comparing normal adults with dementia patients in their abilities to recognize facial emotions, the patients with frontotemporal dementia were seen to have a lower ability to recognize many different emotions. These patients were much less accurate than the control participants (and even in comparison with Alzheimer's patients) in recognizing negative emotions, but were not significantly impaired in recognizing happiness. Anger and disgust in particular were the most difficult for the dementia patients to recognize.

Face recognition is a complex process that is affected by many factors, both environmental and individually internal. Other aspects to be considered include race and culture and their effects on one's ability to recognize faces. Some factors such as the cross-race effect can influence one's ability to recognize and remember faces.

Considerations

Ageing

Research indicates that performance in conjunctive visual search tasks significantly improves during childhood and declines in later life. More specifically, young adults have been shown to have faster reaction times on conjunctive visual search tasks than both children and older adults, but their reaction times were similar for feature visual search tasks. This suggests that there is something about the process of integrating visual features or serial searching that is difficult for children and older adults, but not for young adults. Studies have suggested numerous mechanisms involved in this difficulty in children, including peripheral visual acuity, eye movement ability, ability of attentional focal movement, and the ability to divide visual attention among multiple objects.

Studies have suggested similar mechanisms in the difficulty for older adults, such as age related optical changes that influence peripheral acuity, the ability to move attention over the visual field, the ability to disengage attention, and the ability to ignore distractors.

A study by Lorenzo-López et al. (2008) provides neurological evidence for the fact that older adults have slower reaction times during conjunctive searches compared to young adults. Event-related potentials (ERPs) showed longer latencies and lower amplitudes in older subjects than young adults at the P3 component, which is related to activity of the parietal lobes. This suggests the involvement of the parietal lobe function with an age-related decline in the speed of visual search tasks. Results also showed that older adults, when compared to young adults, had significantly less activity in the anterior cingulate cortex and many limbic and occipitotemporal regions that are involved in performing visual search tasks.

Alzheimer's disease

Research has found that people with Alzheimer's disease (AD) are significantly impaired overall in visual search tasks. People with AD manifest enhanced spatial cueing, but this benefit is only obtained for cues with high spatial precision. Abnormal visual attention may underlie certain visuospatial difficulties in patients with (AD). People with AD have hypometabolism and neuropathology in the parietal cortex, and given the role of parietal function for visual attention, patients with AD may have hemispatial neglect, which may result in difficulty with disengaging attention in visual search.

An experiment conducted by Tales et al. (2000) investigated the ability of patients with AD to perform various types of visual search tasks. Their results showed that search rates on "pop-out" tasks were similar for both AD and control groups, however, people with AD searched significantly slower compared to the control group on a conjunction task. One interpretation of these results is that the visual system of AD patients has a problem with feature binding, such that it is unable to communicate the different feature descriptions for the stimulus efficiently. Binding of features is thought to be mediated by areas in the temporal and parietal cortex, and these areas are known to be affected by AD-related pathology.

Another possibility for the impairment of people with AD on conjunction searches is that there may be some damage to general attentional mechanisms in AD, and therefore any attention-related task will be affected, including visual search.

Tales et al. (2000) detected a double dissociation with their experimental results on AD and visual search. Earlier work was carried out on patients with Parkinson's disease (PD) concerning the impairment patients with PD have on visual search tasks. In those studies, evidence was found of impairment in PD patients on the "pop-out" task, but no evidence was found on the impairment of the conjunction task. As discussed, AD patients show the exact opposite of these results: normal performance was seen on the "pop-out" task, but impairment was found on the conjunction task. This double dissociation provides evidence that PD and AD affect the visual pathway in different ways, and that the pop-out task and the conjunction task are differentially processed within that pathway.

Autism

Studies have consistently shown that autistic individuals performed better and with lower reaction times in feature and conjunctive visual search tasks than matched controls without autism. Several explanations for these observations have been suggested. One possibility is that people with autism have enhanced perceptual capacity. This means that autistic individuals are able to process larger amounts of perceptual information, allowing for superior parallel processing and hence faster target location. Second, autistic individuals show superior performance in discrimination tasks between similar stimuli and therefore may have an enhanced ability to differentiate between items in the visual search display. A third suggestion is that autistic individuals may have stronger top-down target excitation processing and stronger distractor inhibition processing than controls. Keehn et al. (2008) used an event-related functional magnetic resonance imaging design to study the neurofunctional correlates of visual search in autistic children and matched controls of typically developing children. Autistic children showed superior search efficiency and increased neural activation patterns in the frontal, parietal, and occipital lobes when compared to the typically developing children. Thus, autistic individuals' superior performance on visual search tasks may be due to enhanced discrimination of items on the display, which is associated with occipital activity, and increased top-down shifts of visual attention, which is associated with the frontal and parietal areas.

Consumer psychology

In the past decade, there has been extensive research into how companies can maximise sales using psychological techniques derived from visual search to determine how products should be positioned on shelves. Pieters and Warlop (1999) used eye tracking devices to assess saccades and fixations of consumers while they visually scanned/searched an array of products on a supermarket shelf. Their research suggests that consumers specifically direct their attention to products with eye-catching properties such as shape, colour or brand name. This effect is due to a pressured visual search where eye movements accelerate and saccades minimise, thus resulting in the consumer's quickly choosing a product with a 'pop out' effect. This study suggests that efficient search is primarily used, concluding that consumers do not focus on items that share very similar features. The more distinct or maximally visually different a product is from surrounding products, the more likely the consumer is to notice it. Janiszewski (1998) discussed two types of consumer search. One search type is goal directed search taking place when somebody uses stored knowledge of the product in order to make a purchase choice. The second is exploratory search. This occurs when the consumer has minimal previous knowledge about how to choose a product. It was found that for exploratory search, individuals would pay less attention to products that were placed in visually competitive areas such as the middle of the shelf at an optimal viewing height. This was primarily due to the competition in attention meaning that less information was maintained in visual working memory for these products.

E-patient

From Wikipedia, the free encyclopedia https://en.wikipedi...