Visual short-term memory compared in rhesus monkeys and humans

Change detection is a popular task to study visual short-term memory (STM) in humans [1-4]. Much of this work suggests that STM has a fixed capacity of 4 ± 1 items [1-6]. Here we report the first comparison of change-detection memory between humans and a species closely related to humans, the rhesus monkey. Monkeys and humans were tested in nearly identical procedures with overlapping display sizes. Although the monkeys' STM was well fit by a one-item fixed-capacity memory model, other monkey memory tests with four-item lists have shown performance impossible to obtain with a one-item capacity [7]. We suggest that this contradiction can be resolved using a continuous-resource approach more closely tied to the neural basis of memory [8, 9]. In this view, items have a noisy memory representation whose noise level depends on display size as a result of the distributed allocation of a continuous resource. In accord with this theory, we show that performance depends on the perceptual distance between items before and after the change, and d' depends on display size in an approximately power-law fashion. Our results open the door to combining the power of psychophysics, computation, and physiology to better understand the neural basis of STM.     

Ultra-rapid categorization of fourier-spectrum equalized natural images: macaques and humans perform similarly

Background

Comparative studies of cognitive processes find similarities between humans and apes but also monkeys. Even high-level processes, like the ability to categorize classes of object from any natural scene under ultra-rapid time constraints, seem to be present in rhesus macaque monkeys (despite a smaller brain and the lack of language and a cultural background). An interesting and still open question concerns the degree to which the same images are treated with the same efficacy by humans and monkeys when a low level cue, the spatial frequency content, is controlled.

Methodology/Principal Findings

We used a set of natural images equalized in Fourier spectrum and asked whether it is still possible to categorize them as containing an animal and at what speed. One rhesus macaque monkey performed a forced-choice saccadic task with a good accuracy (67.5% and 76% for new and familiar images respectively) although performance was lower than with non-equalized images. Importantly, the minimum reaction time was still very fast (100 ms). We compared the performances of human subjects with the same setup and the same set of (new) images. Overall mean performance of humans was also lower than with original images (64% correct) but the minimum reaction time was still short (140 ms).

Conclusion

Performances on individual images (% correct but not reaction times) for both humans and the monkey were significantly correlated suggesting that both species use similar features to perform the task. A similar advantage for full-face images was seen for both species. The results also suggest that local low spatial frequency information could be important, a finding that fits the theory that fast categorization relies on a rapid feedforward magnocellular signal.     

Replication in abstract and natural systems

Real reproducing systems are contrasted with cellular automata-based models of self-reproduction. It is argued that the reproduction described by the latter is trivial compared to its biological counterpart. The paper explores a few reasons and consequences of this situation, along with a discussion on different forms of the basic reproduction (and construction) process.     

Visual categorization: accessing abstraction in non-human primates

Evolution might have set the basic foundations for abstract mental representation long ago. Because of language, mental abilities would have reached different degrees of sophistication in mammals and in humans but would be, essentially, of the same nature. Thus, humans and animals might rely on the same basic mechanisms that could be masked in humans by the use of sophisticated strategies. In this paper, monkey and human abilities are compared in a variety of perceptual tasks including visual categorization to assess behavioural similarities and dissimilarities, and to determine the level of abstraction of monkeys' mental representations. The question of how these abstract representations might be encoded in the brain is then addressed. A comparative study of the neural processing underlying abstract cognitive operations in animals and humans might help to understand when abstraction emerged in the phylogenetic scale, and how it increased in complexity.     

The Thatcher illusion in humans and monkeys

Primates possess the remarkable ability to differentiate faces of group members and to extract relevant information about the individual directly from the face. Recognition of conspecific faces is achieved by means of holistic processing, i.e. the processing of the face as an unparsed, perceptual whole, rather than as the collection of independent features (part-based processing). The most striking example of holistic processing is the Thatcher illusion. Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 180°), but strikingly grotesque when the face is upright. This effect can be explained by a lack of processing capabilities for locally rotated facial features when the face is turned upside down. Recently, a Thatcher illusion was described in the macaque monkey analogous to that known from human investigations. Using a habituation paradigm combined with eye tracking, we address the critical follow-up questions raised in the aforementioned study to show the Thatcher illusion as a function of the observer''s species (humans and macaques), the stimulus'' species (humans and macaques) and the level of perceptual expertise (novice, expert).     

Reflexive social attention in monkeys and humans

For humans, social cues often guide the focus of attention. Although many nonhuman primates, like humans, live in large, complex social groups, the extent to which human and nonhuman primates share fundamental mechanisms of social attention remains unexplored. Here, we show that, when viewing a rhesus macaque looking in a particular direction, both rhesus macaques and humans reflexively and covertly orient their attention in the same direction. Specifically, when performing a peripheral visual target detection task, viewing a monkey with either its eyes alone or with both its head and eyes averted to one side facilitated the detection of peripheral targets when they randomly appeared on the same side. Moreover, viewing images of a monkey with averted gaze evoked small but systematic shifts in eye position in the direction of gaze in the image. The similar magnitude and temporal dynamics of response facilitation and eye deviation in monkeys and humans suggest shared neural circuitry mediating social attention.     

Cortical representations of pitch in monkeys and humans

Pitch perception is crucial for vocal communication, music perception, and auditory object processing in a complex acoustic environment. How pitch is represented in the cerebral cortex has for a long time remained an unanswered question in auditory neuroscience. Several lines of evidence now point to a distinct non-primary region of auditory cortex in primates that contains a cortical representation of pitch.     

Perception of shape-from-motion in macaque monkeys and humans

Motion is one of the most efficient cues for shape perception. We conducted behavioral experiments to examine how monkeys perceive shapes defined by motion cues and whether they perceive them as humans do. We trained monkeys to perform a shape discrimination task in which shapes were defined by the motion of random dots. Effects of dot density and dot speed on the shape perception of monkeys were examined. Human subjects were also tested using the same paradigm and the test results were compared with those of monkeys. In both monkeys and humans, correct performance rates declined when density or speed of random dots was reduced. Both of them tended to confuse the same combinations of shapes frequently. These results suggest that monkeys and humans perceive shapes defined by motion cues in a similar manner and probably have common neural mechanisms to perceive them. Electronic Publication     

Cooperation and competition in two forest monkeys

Putty-nosed monkeys, Cercopithecus nictitans stampflii, occurat various sites in West Africa, particularly in the transitionzone between rainforest and savannah. The species is sometimesseen in primary rainforest, although at a curiously low densitycompared with that of other monkey species. We conducted a 24-monthfield study in the tropical rainforest of Taï NationalPark, Ivory Coast, and found that putty-nosed monkeys requirean ecological niche almost identical to that of the Diana monkeys,Cercopithecus diana diana. Moreover, the niche breadth of putty-nosedmonkeys was significantly decreased in the presence of Dianamonkeys, suggesting that feeding competition with Diana monkeyskept putty-nosed monkeys from successfully colonizing a rainforesthabitat. However, contrary to the interspecies competition hypothesis,groups of both species almost completely overlapped in homeranges and formed near-permanent mixed-species associations,rather than avoiding each other. We hypothesized that Dianamonkeys tolerated immigrating putty-nosed monkeys and formedmixed-species groups with them, despite high levels of competition,because of their merit in predation defense. Direct observationsand a series of field experiments confirmed that male putty-nosedmonkeys play a vital role in defense against crowned eagles,suggesting that putty-nosed monkeys obtain access to feedingtrees by offering antipredation benefits to Diana monkeys. Wediscuss these findings in light of biological market theory.     

Visual pattern recognition in humans

We have investigated how observers learn to classify compound Gabor signals as a function of their differentiating frequency components. Performance appears to be consistent with decision processes based upon the least squares minimum distance classifier (LSMDC) operating over a cartesian feature space consisting of the real (even) and imaginary (odd) components of the signals. The LSMDC model assumes observers form prototype signals, or adaptive filters, for each signal class in the learing phase, and classify as a function of their degree of match to each prototype. The underlying matching process can be modelled in terms of cross-correlation between prototype images and the input sample.Study supported by Deutsche Forschungsgemeinschaft grants Re 337/3-3 and Po 121/13-1Deutsche Forschungsgemeinschaft Guest-Professor (Mu 93/103-1)     

Common fronto-temporal effective connectivity in humans and monkeys

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Food-exchange with humans in brown capuchin monkeys

To assess how brown capuchin monkeys (Cebus apella) delay gratification and maximize payoff, we carried out four experiments in which six subjects could exchange food pieces with a human experimenter. The pieces differed either in quality or quantity. In qualitative exchanges, all subjects gave a piece of food to receive another of higher value. When the difference of value between the rewards to be returned and those expected was higher, subjects performed better. Only two subjects refrained from nibbling the piece of food before returning it. All subjects performed two or three qualitative exchanges in succession to obtain a given reward. In quantitative exchanges, three subjects returned a food item to obtain a bigger one, but two of them nibbled the item before returning it. Individual differences were marked. Subjects had some difficulties when the food to be returned was similar or equal in quality to that expected.     

Second-order relational manipulations affect both humans and monkeys

Recognition and individuation of conspecifics by their face is essential for primate social cognition. This ability is driven by a mechanism that integrates the appearance of facial features with subtle variations in their configuration (i.e., second-order relational properties) into a holistic representation. So far, there is little evidence of whether our evolutionary ancestors show sensitivity to featural spatial relations and hence holistic processing of faces as shown in humans. Here, we directly compared macaques with humans in their sensitivity to configurally altered faces in upright and inverted orientations using a habituation paradigm and eye tracking technologies. In addition, we tested for differences in processing of conspecific faces (human faces for humans, macaque faces for macaques) and non-conspecific faces, addressing aspects of perceptual expertise. In both species, we found sensitivity to second-order relational properties for conspecific (expert) faces, when presented in upright, not in inverted, orientation. This shows that macaques possess the requirements for holistic processing, and thus show similar face processing to that of humans.     

Conjugated and unconjugated bilirubins in humans and rhesus monkeys. Structural identity of bilirubins from biles and meconiums of newborn humans and rhesus monkeys.

1. Bilirubin-IXalpha monoglucuronide was the predominant bilirubin in biles and meconiums of newborn humans and rhesus monkeys. Rhesus-monkey baby biles contained slightly more diglucuronide than did human baby biles. 2. Bilrubin-IXalpha glucoside, bilirubin-IXalpha xyloside and bilirubin-IXbeta were also constituents of human and rhesus-monkey baby biles and meconiums. Bilirubin-IXalpha glucuronide glucoside was present in human and rhesus-monkey baby biles but not in meconiums. The identity of the bilirubins was confirmed by u.v.-visible and mass spectroscopy of the azodipyrroles obtained by treating the bilirubins with diazotized ethyl anthranilate. The resulting azodipyrroles were identical with the corresponding azodipyrroles obtained from human adult biles and also from reduced isomers of biliverdin. 3. Bilirubin-IXbeta was present in much higher proportions in the extracts of meconiums than in the extracts of biles from the same babies. 4. Oxidation of bilirubins to biliverdins occurs in utero to a small but undetermined extent. The resulting green pigments were present in meconiums collected from the lower small and large intestines of newborn babies and rhesus monkeys. 5. Butanol extracted most of the bilirubins present in biles. This modified method proved to be quick and easy. Little hydrolysis of bilirubins took place during extraction or separation by t.l.c.     

Orientation discrimination and categorization of photographs of natural objects by pigeons

In Experiment 1, pigeons trained to discriminate rightside-up and upside-down orientations of slides of natural scenes with humans successfully transferred to new slides of the same kind. Experiment 2 revealed that both the orientations of the human figures and of the background scenes controlled the discrimination. When they were oppositely oriented, the background orientation cue was dominant. In Experiment 3 slides showing objects on a white background were presented either rightside up or upside down, with each slide presented in one orientation only. One group of pigeons learned to classify the slides according to their orientations. The other group learned to classify the slides according to arbitrary groupings. When the slides were shown rotated by 180 degrees, the latter group continued to discriminate the individual slides (i.e., the pigeons showed orientation invariance). The former group classified the rotated slides according to their orientations (i.e., orientation discrimination). In Experiment 4, pigeons learned the orientation discrimination with separate sets of human and bird figures. Partial reversal training in one object class transferred to the rest of stimuli in this object class but did not to the other object class. These results suggest that pigeons can learn to discriminate photographs on the basis of orientation but that orientation-based equivalence relationship is not formed between object classes.     

Demographic histories of ERV-K in humans, chimpanzees and rhesus monkeys

We detected 19 complete endogenous retroviruses of the K family in the genome of rhesus monkey (Macaca mulatta; RhERV-K) and 12 full length elements in the genome of the common chimpanzee (Pan troglodytes; CERV-K). These sequences were compared with 55 human HERV-K and 20 CERV-K reported previously, producing a total data set of 106 full-length ERV-K genomes. Overall, 61% of the human elements compared to 21% of the chimpanzee and 47% of rhesus elements had estimated integration times less than 4.5 million years before present (MYBP), with an average integration times of 7.8 MYBP, 13.4 MYBP and 10.3 MYBP for HERV-K, CERV-K and RhERV-K, respectively. By excluding those ERV-K sequences generated by chromosomal duplication, we used 63 of the 106 elements to compare the population dynamics of ERV-K among species. This analysis indicated that both HERV-K and RhERV-K had similar demographic histories, including markedly smaller effective population sizes, compared to CERV-K. We propose that these differing ERV-K dynamics reflect underlying differences in the evolutionary ecology of the host species, such that host ecology and demography represent important determinants of ERV-K dynamics.     

Visual cortex encodes timing information in humans and mice

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