A Medley of Potpourri

Isotope	Abundance	Half-life (t_1/2)	Decay mode	Product
¹⁵⁰Eu	syn	36.9 y	ε	¹⁵⁰Sm
¹⁵¹Eu	47.8%	5×10¹⁸ y	α	¹⁴⁷Pm
¹⁵²Eu	syn	13.54 y	ε	¹⁵²Sm
¹⁵²Eu	syn	13.54 y	β⁻	¹⁵²Gd
¹⁵³Eu	52.2%	stable
¹⁵⁴Eu	syn	8.59 y	β⁻	¹⁵⁴Gd
¹⁵⁵Eu	syn	4.76 y	β⁻	¹⁵⁵Gd

Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanthanide, as it can be dented with a finger nail and easily cut with a knife. When oxidation is removed a shiny-white metal is visible. Europium was isolated in 1901 and is named after the continent of Europe. Being a typical member of the lanthanide series, europium usually assumes the oxidation state +3, but the oxidation state +2 is also common. All europium compounds with oxidation state +2 are slightly reducing. Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the rarest of rare earth elements on Earth and among the least abundant elements in the universe; only about 5×10⁻⁸% of all matter in the universe is europium.

Characteristics

Physical properties

About 300 g of dendritic sublimated 99.998% pure europium handled in a glove box

Oxidized europium, coated with yellow europium(II) carbonate

Europium is a ductile metal with a hardness similar to that of lead. It crystallizes in a body-centered cubic lattice. Some properties of europium are strongly influenced by its half-filled electron shell. Europium has the second lowest melting point and the lowest density of all lanthanides.

Europium becomes a superconductor when it is cooled below 1.8 K and compressed to above 80 GPa. This occurs because europium is divalent in the metallic state, and is converted into the trivalent state by the applied pressure. In the divalent state, the strong local magnetic moment (J = ⁷/₂) suppresses the superconductivity, which is induced by eliminating this local moment (J = 0 in Eu³⁺).

Chemical properties

Europium is the most reactive rare-earth element. It rapidly oxidizes in air, so that bulk oxidation of a centimeter-sized sample occurs within several days. Its reactivity with water is comparable to that of calcium, and the reaction is

2 Eu + 6 H₂O → 2 Eu(OH)₃ + 3 H₂

Because of the high reactivity, samples of solid europium rarely have the shiny appearance of the fresh metal, even when coated with a protective layer of mineral oil. Europium ignites in air at 150 to 180 °C to form europium(III) oxide:

4 Eu + 3 O₂ → 2 Eu₂O₃

Europium dissolves readily in dilute sulfuric acid to form pale pink solutions of the hydrated Eu(III), which exist as a nonahydrate:

2 Eu + 3 H₂SO₄ + 18 H₂O →

2 [Eu(H₂O)₉]³⁺ + 3 SO²⁻
₄ + 3 H₂

Eu(II) vs. Eu(III)

Although usually trivalent, europium readily forms divalent compounds. This behavior is unusual for most lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has an electron configuration 4f⁷ because the half-filled f-shell provides more stability. In terms of size and coordination number, europium(II) and barium(II) are similar. The sulfates of both barium and europium(II) are also highly insoluble in water. Divalent europium is a mild reducing agent, oxidizing in air to form Eu(III) compounds. In anaerobic, and particularly geothermal conditions, the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline earths. This ion-exchange process is the basis of the "negative europium anomaly", the low europium content in many lanthanide minerals such as monazite, relative to the chondritic abundance. Bastnäsite tends to show less of a negative europium anomaly than does monazite, and hence is the major source of europium today. The development of easy methods to separate divalent europium from the other (trivalent) lanthanides made europium accessible even when present in low concentration, as it usually is.

Isotopes

Naturally occurring europium is composed of 2 isotopes, ¹⁵¹Eu and ¹⁵³Eu, with ¹⁵³Eu being the most abundant (52.2% natural abundance). While ¹⁵³Eu is stable, ¹⁵¹Eu was recently found to be unstable to alpha decay with a half-life of 5+11
−3×10¹⁸ years, giving about 1 alpha decay per two minutes in every kilogram of natural europium. This value is in reasonable agreement with theoretical predictions. Besides the natural radioisotope ¹⁵¹Eu, 35 artificial radioisotopes have been characterized, the most stable being ¹⁵⁰Eu with a half-life of 36.9 years, ¹⁵²Eu with a half-life of 13.516 years, and ¹⁵⁴Eu with a half-life of 8.593 years. All the remaining radioactive isotopes have half-lives shorter than 4.7612 years, and the majority of these have half-lives shorter than 12.2 seconds. This element also has 8 meta states, with the most stable being ^150mEu (t_1/2=12.8 hours), ^152m1Eu (t_1/2=9.3116 hours) and ^152m2Eu (t_1/2=96 minutes).

The primary decay mode for isotopes lighter than ¹⁵³Eu is electron capture, and the primary mode for heavier isotopes is beta minus decay. The primary decay products before ¹⁵³Eu are isotopes of samarium (Sm) and the primary products after are isotopes of gadolinium (Gd).

Europium as a nuclear fission product

Europium is produced by nuclear fission, but the fission product yields of europium isotopes are low near the top of the mass range for fission products.

As with other lanthanides, many isotopes of europium, especially those that have odd mass numbers or are neutron-poor like. ¹⁵²Eu, have high cross sections for neutron capture, often high enough to be neutron poisons.

¹⁵¹Eu is the beta decay product of samarium-151, but since this has a long decay half-life and short mean time to neutron absorption, most ¹⁵¹Sm instead ends up as ¹⁵²Sm.

¹⁵²Eu (half-life 13.516 years) and ¹⁵⁴Eu (half-life 8.593 years) cannot be beta decay products because ¹⁵²Sm and ¹⁵⁴Sm are non-radioactive, but ¹⁵⁴Eu is the only long-lived "shielded" nuclide, other than ¹³⁴Cs, to have a fission yield of more than 2.5 parts per million fissions. A larger amount of ¹⁵⁴Eu is produced by neutron activation of a significant portion of the non-radioactive ¹⁵³Eu; however, much of this is further converted to ¹⁵⁵Eu.

¹⁵⁵Eu (half-life 4.7612 years) has a fission yield of 330 parts per million (ppm) for uranium-235 and thermal neutrons; most of it is transmuted to non-radioactive and nonabsorptive gadolinium-156 by the end of fuel burnup.

Overall, europium is overshadowed by caesium-137 and strontium-90 as a radiation hazard, and by samarium and others as a neutron poison.

Occurrence

Monazite

Europium is not found in nature as a free element. Many minerals contain europium, with the most important sources being bastnäsite, monazite, xenotime and loparite-(Ce). No europium-dominant minerals are known yet, despite a single find of a tiny possible Eu–O or Eu–O–C system phase in the Moon's regolith.

Depletion or enrichment of europium in minerals relative to other rare-earth elements is known as the europium anomaly. Europium is commonly included in trace element studies in geochemistry and petrology to understand the processes that form igneous rocks (rocks that cooled from magma or lava). The nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks. The average crustal abundance of europium is 2-2.2 ppm.

Divalent europium (Eu²⁺) in small amounts is the activator of the bright blue fluorescence of some samples of the mineral fluorite (CaF₂). The reduction from Eu³⁺ to Eu²⁺ is induced by irradiation with energetic particles. The most outstanding examples of this originated around Weardale and adjacent parts of northern England; it was the fluorite found here that fluorescence was named after in 1852, although it was not until much later that europium was determined to be the cause.

In astrophysics, the signature of europium in stellar spectra can be used to classify stars and inform theories of how or where a particular star was born. For instance, astronomers recently identified higher-than-expected levels of europium within the star J1124+4535, hypothesizing that this star originated in a dwarf galaxy that collided with the Milky Way billions of years ago.

Production

Europium is associated with the other rare-earth elements and is, therefore, mined together with them. Separation of the rare-earth elements occurs during later processing. Rare-earth elements are found in the minerals bastnäsite, loparite-(Ce), xenotime, and monazite in mineable quantities. Bastnäsite is a group of related fluorocarbonates, Ln(CO₃)(F,OH). Monazite is a group of related of orthophosphate minerals LnPO
₄ (Ln denotes a mixture of all the lanthanides except promethium), loparite-(Ce) is an oxide, and xenotime is an orthophosphate (Y,Yb,Er,...)PO₄. Monazite also contains thorium and yttrium, which complicates handling because thorium and its decay products are radioactive. For the extraction from the ore and the isolation of individual lanthanides, several methods have been developed. The choice of method is based on the concentration and composition of the ore and on the distribution of the individual lanthanides in the resulting concentrate. Roasting the ore, followed by acidic and basic leaching, is used mostly to produce a concentrate of lanthanides. If cerium is the dominant lanthanide, then it is converted from cerium(III) to cerium(IV) and then precipitated. Further separation by solvent extractions or ion exchange chromatography yields a fraction which is enriched in europium. This fraction is reduced with zinc, zinc/amalgam, electrolysis or other methods converting the europium(III) to europium(II). Europium(II) reacts in a way similar to that of alkaline earth metals and therefore it can be precipitated as a carbonate or co-precipitated with barium sulfate.^[35] Europium metal is available through the electrolysis of a mixture of molten EuCl₃ and NaCl (or CaCl₂) in a graphite cell, which serves as cathode, using graphite as anode. The other product is chlorine gas.

A few large deposits produce or produced a significant amount of the world production. The Bayan Obo iron ore deposit contains significant amounts of bastnäsite and monazite and is, with an estimated 36 million tonnes of rare-earth element oxides, the largest known deposit. The mining operations at the Bayan Obo deposit made China the largest supplier of rare-earth elements in the 1990s. Only 0.2% of the rare-earth element content is europium. The second large source for rare-earth elements between 1965 and its closure in the late 1990s was the Mountain Pass rare earth mine. The bastnäsite mined there is especially rich in the light rare-earth elements (La-Gd, Sc, and Y) and contains only 0.1% of europium. Another large source for rare-earth elements is the loparite found on the Kola peninsula. It contains besides niobium, tantalum and titanium up to 30% rare-earth elements and is the largest source for these elements in Russia.

Compounds

Europium sulfate, Eu₂(SO₄)₃

Europium sulfate fluorescing red under ultraviolet light

Europium compounds tend to exist trivalent oxidation state under most conditions. Commonly these compounds feature Eu(III) bound by 6–9 oxygenic ligands, typically water. These compounds, the chlorides, sulfates, nitrates, are soluble in water or polar organic solvent. Lipophilic europium complexes often feature acetylacetonate-like ligands, e.g., Eufod.

Halides

Europium metal reacts with all the halogens:

2 Eu + 3 X₂ → 2 EuX₃ (X = F, Cl, Br, I)

This route gives white europium(III) fluoride (EuF₃), yellow europium(III) chloride (EuCl₃), gray europium(III) bromide (EuBr₃), and colorless europium(III) iodide (EuI₃). Europium also forms the corresponding dihalides: yellow-green europium(II) fluoride (EuF₂), colorless europium(II) chloride (EuCl₂), colorless europium(II) bromide (EuBr₂), and green europium(II) iodide (EuI₂).

Chalcogenides and pnictides

Europium forms stable compounds with all of the chalcogens, but the heavier chalcogens (S, Se, and Te) stabilize the lower oxidation state. Three oxides are known: europium(II) oxide (EuO), europium(III) oxide (Eu₂O₃), and the mixed-valence oxide Eu₃O₄, consisting of both Eu(II) and Eu(III). Otherwise, the main chalcogenides are europium(II) sulfide (EuS), europium(II) selenide (EuSe) and europium(II) telluride (EuTe): all three of these are black solids. EuS is prepared by sulfiding the oxide at temperatures sufficiently high to decompose the Eu₂O₃:

Eu₂O₃ + 3 H₂S → 2 EuS + 3 H₂O + S

The main nitride is europium(III) nitride (EuN).

History

Although europium is present in most of the minerals containing the other rare elements, due to the difficulties in separating the elements it was not until the late 1800s that the element was isolated. William Crookes observed the phosphorescent spectra of the rare elements including those eventually assigned to europium.

Europium was first found in 1892 by Paul Émile Lecoq de Boisbaudran, who obtained basic fractions from samarium-gadolinium concentrates which had spectral lines not accounted for by samarium or gadolinium. However, the discovery of europium is generally credited to French chemist Eugène-Anatole Demarçay, who suspected samples of the recently discovered element samarium were contaminated with an unknown element in 1896 and who was able to isolate it in 1901; he then named it europium.

When the europium-doped yttrium orthovanadate red phosphor was discovered in the early 1960s, and understood to be about to cause a revolution in the color television industry, there was a scramble for the limited supply of europium on hand among the monazite processors, as the typical europium content in monazite is about 0.05%. However, the Molycorp bastnäsite deposit at the Mountain Pass rare earth mine, California, whose lanthanides had an unusually high europium content of 0.1%, was about to come on-line and provide sufficient europium to sustain the industry. Prior to europium, the color-TV red phosphor was very weak, and the other phosphor colors had to be muted, to maintain color balance. With the brilliant red europium phosphor, it was no longer necessary to mute the other colors, and a much brighter color TV picture was the result. Europium has continued to be in use in the TV industry ever since as well as in computer monitors. Californian bastnäsite now faces stiff competition from Bayan Obo, China, with an even "richer" europium content of 0.2%.

Frank Spedding, celebrated for his development of the ion-exchange technology that revolutionized the rare-earth industry in the mid-1950s, once related the story of how he was lecturing on the rare earths in the 1930s, when an elderly gentleman approached him with an offer of a gift of several pounds of europium oxide. This was an unheard-of quantity at the time, and Spedding did not take the man seriously. However, a package duly arrived in the mail, containing several pounds of genuine europium oxide. The elderly gentleman had turned out to be Herbert Newby McCoy, who had developed a famous method of europium purification involving redox chemistry.

Applications

Europium is one of the elements involved in emitting red light in CRT televisions.

Relative to most other elements, commercial applications for europium are few and rather specialized. Almost invariably, its phosphorescence is exploited, either in the +2 or +3 oxidation state.

It is a dopant in some types of glass in lasers and other optoelectronic devices. Europium oxide (Eu₂O₃) is widely used as a red phosphor in television sets and fluorescent lamps, and as an activator for yttrium-based phosphors. Color TV screens contain between 0.5 and 1 g of europium oxide. Whereas trivalent europium gives red phosphors, the luminescence of divalent europium depends strongly on the composition of the host structure. UV to deep red luminescence can be achieved. The two classes of europium-based phosphor (red and blue), combined with the yellow/green terbium phosphors give "white" light, the color temperature of which can be varied by altering the proportion or specific composition of the individual phosphors. This phosphor system is typically encountered in helical fluorescent light bulbs. Combining the same three classes is one way to make trichromatic systems in TV and computer screens, but as an additive, it can be particularly effective in improving the intensity of red phosphor. Europium is also used in the manufacture of fluorescent glass, increasing the general efficiency of fluorescent lamps. One of the more common persistent after-glow phosphors besides copper-doped zinc sulfide is europium-doped strontium aluminate. Europium fluorescence is used to interrogate biomolecular interactions in drug-discovery screens. It is also used in the anti-counterfeiting phosphors in euro banknotes.

An application that has almost fallen out of use with the introduction of affordable superconducting magnets is the use of europium complexes, such as Eu(fod)₃, as shift reagents in NMR spectroscopy. Chiral shift reagents, such as Eu(hfc)₃, are still used to determine enantiomeric purity.

A recent (2015) application of europium is in quantum memory chips which can reliably store information for days at a time; these could allow sensitive quantum data to be stored to a hard disk-like device and shipped around.

Precautions

**Europium**
Hazards
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H250
GHS precautionary statements	P222, P231, P422
NFPA 704	3 0 1 W

There are no clear indications that europium is particularly toxic compared to other heavy metals. Europium chloride, nitrate and oxide have been tested for toxicity: europium chloride shows an acute intraperitoneal LD₅₀ toxicity of 550 mg/kg and the acute oral LD₅₀ toxicity is 5000 mg/kg. Europium nitrate shows a slightly higher intraperitoneal LD₅₀ toxicity of 320 mg/kg, while the oral toxicity is above 5000 mg/kg. The metal dust presents a fire and explosion hazard.

Dog intelligence

From Wikipedia, the free encyclopedia

Many dogs can follow a human pointing gesture.

Dog intelligence or dog cognition is the process in dogs of acquiring, storing in memory, retrieving, combining, comparing, and using in new situations information and conceptual skills.

Studies have shown that dogs display many behaviors associated with intelligence. They have advanced memory skills, and are able to read and react appropriately to human body language such as gesturing and pointing, and to understand human voice commands. Dogs demonstrate a theory of mind by engaging in deception.

Evolutionary perspective

Dogs have often been used in studies of cognition, including research on perception, awareness, memory, and learning, notably research on classical and operant conditioning. In the course of this research, behavioral scientists uncovered a surprising set of social-cognitive abilities in the domestic dog, abilities that are neither possessed by dogs' closest canine relatives nor by other highly intelligent mammals such as great apes. Rather, these skills resemble some of the social-cognitive skills of human children. This may be an example of Convergent evolution, which happens when distantly related species independently evolve similar solutions to the same problems. For example, fish, penguins and dolphins have each separately evolved flippers as solution to the problem of moving through the water. With dogs and humans, we may see psychological convergence; that is, dogs have evolved to be cognitively more similar to humans than we are to our closest genetic relatives.

However, it is questionable whether the cognitive evolution of humans and animals may be called "independent". The cognitive capacities of dogs have inevitably been shaped by millennia of contact with humans. As a result of this physical and social evolution, many dogs readily respond to social cues common to humans, quickly learn the meaning of words, show cognitive bias and exhibit emotions that seem to reflect those of humans.

Research suggests that domestic dogs may have lost some of their original cognitive abilities once they joined humans. For example, one study showed compelling evidence that dingos (Canis dingo) can outperform domestic dogs in non-social problem-solving experiments. Another study indicated that after being trained to solve a simple manipulation task, dogs that are faced with an unsolvable version of the same problem look at a nearby human, while socialized wolves do not. Thus, modern domestic dogs seem to use humans to solve some of their problems for them.

In 2014, a whole genome study of the DNA differences between wolves and dogs found that dogs did not show a reduced fear response, they showed greater synaptic plasticity. Synaptic plasticity is widely believed to be the cellular correlate of learning and memory, and this change may have altered the learning and memory abilities of dogs.

Most modern research on dog cognition has focused on pet dogs living in human homes in developed countries, which is only a small fraction of the dog population and dogs from other populations may show different cognitive behaviors. Breed differences possibly could impact on spatial learning and memory abilities.

Studies history

The first intelligence test for dogs was developed in 1976. It included measurements of short-term memory, agility, and ability to solve problems such as detouring to a goal. It also assessed the ability of a dog to adapt to new conditions and cope with emotionally difficult situations. The test was administered to 100 dogs and standardized, and breed norms were developed. Stanley Coren used surveys done by dog obedience judges to rank dog breeds by intelligence and published the results in his book The Intelligence of Dogs.

Perception

Perception refers to mental processes through which incoming sensory information is organized and interpreted in order to represent and understand the environment. Perception includes such processes as the selection of information through attention, the organization of sensory information through grouping, and the identification of events and objects. In the dog, olfactory information (the sense of smell) is particularly salient (compared with humans) but the dogs senses also include vision, hearing, taste, touch and proprioception. There is also evidence that dogs sense the earth's magnetic field.

One researcher has proposed that dogs perceive the passing of time through the dissipation of smells.

Awareness

The concept of "object permanence" refers to the ability of an animal to understand that objects continue to exist even when they have moved outside of their field of view. This ability is not present at birth, and developmental psychologist Jean Piaget described six stages in the development of object permanence in human infants. A similar approach has been used with dogs, and there is evidence that dogs go through similar stages and reach the advanced fifth stage by an age of 8 weeks. At this stage they can track "successive visible displacement" in which the experimenter moves the object behind multiple screens before leaving it behind the last one. It is unclear whether dogs reach Stage 6 of Piaget's object permanence development model.

A study in 2013 indicated that dogs appear to recognize other dogs regardless of breed, size, or shape, and distinguish them from other animals.

In 2014, a study using magnetic resonance imaging demonstrated that voice-response areas exist in the brains of dogs and that they show a response pattern in the anterior temporal voice areas that is similar to that in humans.

Social cognition

Social learning: observation and rank

An English Springer Spaniel taking cues from its master.

Dogs are capable of learning through simple reinforcement (e.g., classical or operant conditioning), but they also learn by watching humans and other dogs.

One study investigated whether dogs engaged in partnered play would adjust their behavior to the attention-state of their partner. The experimenters observed that play signals were only sent when the dog was holding the attention of its partner. If the partner was distracted, the dog instead engaged in attention-getting behavior before sending a play signal.

Puppies learn behaviors quickly by following examples set by experienced dogs. This form of intelligence is not particular to those tasks dogs have been bred to perform, but can be generalized to various abstract problems. For example, Dachshund puppies were set the problem of pulling a cart by tugging on an attached piece of ribbon in order to get a reward from inside the cart. Puppies that watched an experienced dog perform this task learned the task fifteen times faster than those left to solve the problem on their own.

The social rank of dogs affects their performance in social learning situations. In social groups with a clear hierarchy, dominant individuals are the more influential demonstrators and the knowledge transfer tends to be unidirectional, from higher rank to lower. In a problem-solving experiment, dominant dogs generally performed better than subordinates when they observed a human demonstrator's actions, a finding that reflects the dominance of the human in dog-human groups. Subordinate dogs learn best from the dominant dog that is adjacent in the hierarchy.

Following human cues

Dogs show human-like social cognition in various ways. For example, dogs can react appropriately to human body language such as gesturing and pointing, and they also understand human voice commands. For example, in one study, puppies were presented with a box, and shown that, when a handler pressed a lever, a ball would roll out of the box. The handler then allowed the puppy to play with the ball, making it an intrinsic reward. The pups were then allowed to interact with the box. Roughly three quarters of the puppies subsequently touched the lever, and over half successfully released the ball, compared to only 6% in a control group that did not watch the human manipulate the lever.

Similarly, dogs may be guided by cues indicating the direction of a human's attention. In one task a reward was hidden under one of two buckets. The experimenter then indicated the location of the reward by tapping the bucket, pointing to the bucket, nodding at the bucket, or simply looking at the bucket. The dogs followed these signals, performing better than chimpanzees, wolves, and human infants at this task; even puppies with limited exposure to humans performed well.

Dogs can follow the direction of pointing by humans. New Guinea singing dogs are a half-wild proto-dog endemic to the remote alpine regions of New Guinea and these can follow human pointing as can Australian dingoes. These both demonstrate an ability to read human gestures that arose early in domestication without human selection. Dogs and wolves have also been shown to follow more complex pointing made with body parts other than the human arm and hand (e.g. elbow, knee, foot). Dogs tend to follow hand/arm pointed directions more when combined with eye signaling as well. In general, dogs seems to use human cues as an indication on where to go and what to do. Overall, dogs appear to have several cognitive skills necessary to understand communication as information; however, findings on dogs' understanding of referentiality and others' mental states are controversial and it is not clear whether dog themselves communicate with informative motives.

For canines to perform well on traditional human-guided tasks (e.g. following the human point) both relevant lifetime experiences with humans—including socialization to humans during the critical phase for social development—and opportunities to associate human body parts with certain outcomes (such as food being provided by humans, a human throwing or kicking a ball, etc.) are required.

In 2016, a study of water rescue dogs that respond to words or gestures found that the dogs would respond to the gesture rather than the verbal command.

Memory

Episodic memory

Dogs have demonstrated episodic-like memory by recalling past events that included the complex actions of humans. In a 2019 study, a correlation has been shown between the size of the dog and the functions of memory and self-control, with larger dogs performing significantly better than smaller dogs in these functions. However, in the study brain size did not predict a dog's ability to follow human pointing gestures, nor was it associated with their inferential and physical reasoning abilities.

Learning and using words

Various studies have shown that dogs readily learn the names of objects and can retrieve an item from among many others when given its name. For example, in 2008, Betsy, a Border Collie, knew over 340 words by the retrieval test, and she was also able to connect an object with a photographic image of the object, despite having seen neither before. In another study, a dog watched as experimenters handed an object back and forth to each other while using the object's name in a sentence. The dog subsequently retrieved the item given its name.

In humans, "fast mapping" is the ability to form quick and rough hypotheses about the meaning of a new word after only a single exposure. In 2004, a study with Rico, a Border Collie, showed he was able to fast map. Rico initially knew the labels of over 200 items. He inferred the names of novel items by exclusion, that is, by knowing that the novel item was the one that he did not already know. Rico correctly retrieved such novel items immediately and four weeks after the initial exposure. Rico was also able to interpret phrases such as "fetch the sock" by its component words (rather than considering its utterance to be a single word). Rico could also give the sock to a specified person. This performance is comparable to that of 3-year-old humans.

In 2013, a study documented the learning and memory capabilities of a border collie, "Chaser", who had learned the names and could associate by verbal command over 1,000 words at the time of its publishing. Chaser was documented as capable of learning the names of new objects "by exclusion", and capable of linking nouns to verbs. It is argued that central to the understanding of the border collie's remarkable accomplishments is the dog's breeding background—collies bred for herding work are uniquely suited for intellectual tasks like word association which may require the dog to work "at a distance" from their human companions, and the study credits this dog's selective breeding in addition to rigorous training for her intellectual prowess.

Emotional intelligence

Studies suggest that dogs feel complex emotions, like jealousy and anticipation. However, behavioral evidence of seemingly human emotions must be interpreted with care. For example, in his 1996 book Good Natured, ethologist Frans de Waal discusses an experiment on guilt and reprimands conducted on a female Siberian Husky. The dog had the habit of shredding newspapers, and when her owner returned home to find the shredded papers and scold her she would act guilty. However, when the owner himself shredded the papers without the dog's knowledge, the dog "acted just as 'guilty' as when she herself had created the mess." De Waal concludes that the dog did not display true guilt as humans understand it, but rather simply the anticipation of reprimand.

One limitation in the study of emotions in non-human animals, is that they cannot verbalise to express their feelings. However, dogs' emotions can be studied indirectly through cognitive tests, called cognitive bias test, which measure a cognitive bias and allow to make inference about the mood of the animal. Researchers have found that dogs suffering from separation anxiety have a more negative cognitive bias, compared to dogs without separation anxiety. On the other hand, when dogs' separation anxiety is treated with medications and behaviour therapy, their cognitive bias becomes less negative than before treatment. Also administration of oxytocin, rather than a placebo, induces a more positive cognitive bias and positive expectation in dogs. It is therefore suggested that the cognitive bias test can be used to monitor positive emotional states and therefore welfare in dogs.

There is evidence that dogs can discriminate the emotional expressions of human faces. In addition, they seem to respond to faces in somewhat the same way as humans. For example, humans tend to gaze at the right side of a person's face, which may be related to the use of right brain hemisphere for facial recognition. Research indicates that dogs also fixate the right side of a human face, but not that of other dogs or other animals. Dogs are the only non-primate species known to do so.

Problem solving

Sex-specific dynamics are an important contributor to individual differences in cognitive performance of pet dogs in repeated problem-solving tasks.

Captive-raised dingoes (Canis dingo) can outperform domestic dogs in non-social problem-solving. Another study indicated that after undergoing training to solve a simple manipulation task, dogs faced with an unsolvable version of the same problem look at the human, whereas socialized wolves do not. Modern domestic dogs use humans to solve their problems for them.

Learning by inference

Dogs have been shown to learn by making inferences in a similar way to children.

Dogs have the ability to train themselves and learn behaviors through interacting and watching other dogs.

Theory of mind

"Theory of mind" is the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires, intentions, and perspectives that are different from one's own. There is some evidence that dogs demonstrate a theory of mind by engaging in deception. For example, one observer reported that a dog hid a stolen treat by sitting on it until the rightful owner of the treat left the room. Although this could have been accidental, it suggests that the thief understood that the treat's owner would be unable to find the treat if it were out of view. A study found that dogs are able to discriminate an object that a human partner is looking for based on its relevance for the partner and they are more keen on indicating an object that is relevant to the partner compared to an irrelevant one; this suggests that dogs might have a rudimental version of some of the skills necessary for theory of mind.