Spatial frequency and global-local visual processing in capuchin monkeys (Sapajus spp.) and humans (Homo sapiens).

Two experiments employing an identity matching-to-sample procedure were carried out to clarify the factors affecting global-local visual processing of capuchin monkeys (Sapajus spp.) in comparison with humans. In the first experiment, we assessed the relative ability of the two species to discriminate high, medium, or low spatial frequencies (HSFs, MSFs, or LSFs). Then, in a second experiment, we determined if the use of a procedure designed to induce a bias toward attending given spatial frequencies could produce a top-down or selection-history modulation of global-local visual processing in capuchins and humans. In the first experiment, monkeys discriminated better HSFs. By contrast, humans discriminated better MSFs and LSFs. The second experiment showed an effect of SF processing on global-local processing in both species. However, this effect was confined to local trials only and occurred under different conditions in the two species. In monkeys, it occurred following a bias toward attending HSFs, whereas in humans, it occurred following a bias toward attending LSFs. These results provide new information about the relative sensitivity of humans and capuchins to different spatial frequencies in vision. Moreover, they suggest that global-local visual processing can be modulated in both humans and monkeys by processes that are not confined to attending one or the other level of stimulus structure. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Versatile grasping ability in power-grip actions by tufted capuchin monkeys (Sapajus spp.).

OBJECTIVES: Capuchin monkeys are well known to have a high degree of manual dexterity. In this study, we assessed the variability of capuchin grasping actions involving power grips, i.e., manual actions in which the object is grasped between the palm and one or several parts of the fingers and that do not necessarily involve individually controlled finger movements. Planning abilities in executing actions were also evaluated. METHODS: Twenty tufted capuchins (Sapajus spp.) were tested in a task requiring individuals to grasp a dowel inserted into a vertical tube. We examined their grasping techniques, focusing on the following aspects: (i) the different hand postures made during grasping, (ii) the frequency of thumb use in opposition to the other fingers, (iii) the asymmetric use of the hands, and (iv) the configuration of the grasping action for the purpose of comfortably bringing the food to the mouth. RESULTS: Eight power-grip variants were identified, with individual capuchins performing an average of more than five different grips. The use of the thumb in opposition to the other areas of the hand, as reported in studies of precision grips, also appears to be a common feature in power grips. No evidence of group-level manual asymmetries was found. Adult capuchins were better than immature individuals in planning grasping actions in relation to following task demands. DISCUSSION: Overall, these findings clarify the extent to which manual dexterity and cognitive abilities can be expressed in the grasping tasks of highly manually skilled primate species.

Effects of pattern redundancy and hierarchical grouping on global-local visual processing in monkeys (Cebus apella) and humans (Homo sapiens).

Using a Matching-To-Sample (MTS) procedure we assessed the effects of stimulus redundancy, defined on the basis of the information-theory approach to shape goodness proposed by Garner (1974) [20], and grouping on the processing of hierarchical visual patterns in capuchin monkeys and humans. In a first experiment, the MTS performance of both capuchin monkeys and humans benefitted from stimulus redundancy. Moreover, a local advantage in capuchins was observed with visual patterns that required grouping at both global and local level. In a second experiment we eliminated the requirement to group at the local level. This was done to determine if the effects of redundancy would have been evident in condition more similar to those used in previous studies of global-local processing in a comparative context. The benefits of stimulus redundancy emerged again in both species but were confined to local processing in monkeys and to global processing in humans. A local advantage was observed in both species. In a third experiment, the reduction of the size of the stimuli and the increase of the quantity of the local elements produced a shift to global dominance in humans but the local dominance in monkeys was preserved. The implications of these results are discussed in relation to other similarities and differences in higher visual functions in humans and monkeys.

Attention allocation modulates the processing of hierarchical visual patterns: a comparative analysis of capuchin monkeys (Cebus apella) and humans.

Humans show a global advantage when processing hierarchical visual patterns, and they detect the global level of stimulus structure more accurately and faster than the local level in several stimulus contexts. By contrast, capuchins (Cebus apella) and other monkey species show a strong local advantage. A key factor which, if manipulated, could cause an inversion of this effect in monkeys is still to be found. In this study, we examined whether it was possible to induce attention allocation to global and local levels of perceptual analysis in capuchin monkeys and if by doing so, their local dominance could be reversed. We manipulated attentional bias using a matching-to-sample (MTS) task where the proportion of trials requiring global and local processing varied between conditions. The monkeys were compared with humans tested with the same paradigm. Monkeys showed a local advantage in the local bias condition but a global advantage in the global bias condition. The role of attention in processing was confined to the local trials in a first phase of testing but extended to both local and global trials in the course of task practice. Humans exhibited an overall global dominance and an effect of attentional bias on the speed of processing of the global and local level of the stimuli. These results indicate a role for attention in the processing of hierarchical stimuli in monkeys and are discussed in relation to the extent to which they can explain the differences between capuchin monkeys and humans observed in this and other studies.

Processing of visual hierarchical stimuli by fish (Xenotoca eiseni).

Three experiments were designed to investigate visual processing of global and local dimensions of hierarchical stimuli in fish (Xenotoca eiseni). In the first experiment, fish were trained to discriminate between a circle made of circle elements and a cross made of cross elements (consistent stimuli), and tested with a circle made of crosses and a cross made of circles (inconsistent stimuli) to asses their global/local encoding preferences. Fish were also tested for their ability to discriminate single-element shapes. The second and the third experiments manipulated the density of the local elements (Experiment 2) and the size of the global and local shapes of the stimuli (Experiment 3) to assess whether these variables could affect global or local perception of hierarchical visual patterns in fish. In all the experiments, fish showed a global preference irrespective of the density and the size of the stimuli. This preference was not because of an inability to perceive the local constituents of the stimulus, since both fish trained with consistent and fish trained with inconsistent figures showed a clear capacity to discriminate between single-element shapes. Overall, these results suggest that a global preference is not a unique trait of human beings and that differences among different vertebrate species in the global/local strategies of stimulus encoding may be because of different ecological adaptations making initial elaboration of a visual scene in a global or local way more likely.

Picture processing in tufted capuchin monkeys (Cebus apella).

Although pictures are frequently used in place of real objects to investigate various aspects of cognition in different non-human species, there is little evidence that animals treat pictorial stimuli as representations of the real objects. In the present study, we carried out four experiments designed to assess picture processing in tufted capuchin monkeys (Cebus apella), using a simultaneous Matching-to-Sample (MTS) task. The results of the first three experiments indicate that capuchins are able to match objects with their colour photographs and vice versa, and that object-picture matching in this New World monkey species is not due to picture-object confusion. The results of the fourth experiment show that capuchins are able to recognize objects in their pictures with a high level of accuracy even when less realistic images, such as black-and-white photographs, silhouettes and line drawings, are employed as bi-dimensional stimuli. Overall, these findings indicate that capuchin monkeys are able to establish a correspondence between the real objects and their pictorial representations.

The relative use of proximity, shape similarity, and orientation as visual perceptual grouping cues in tufted capuchin monkeys (Cebus apella) and humans (Homo sapiens).

Recent experimental results suggest that human and nonhuman primates differ in how they process visual information to assemble component parts into global shapes. To assess whether some of the observed differences in perceptual grouping could be accounted for by the prevalence of different grouping factors in different species, we carried out 2 experiments designed to evaluate the relative use of proximity, similarity of shape, and orientation as grouping cues in humans (Homo sapiens) and capuchin monkeys (Cebus apella). Both species showed similarly high levels of accuracy using proximity as a cue. Moreover, for both species, grouping by orientation similarity produced a lower level of performance than grouping by proximity. Differences emerged with respect to the use of shape similarity as a cue. In humans, grouping by shape similarity also proved less effective than grouping by proximity but the same was not observed in capuchins. These results suggest that there may be subtle differences between humans and capuchin monkeys in the weighting assigned to different grouping cues that may affect the way in which they combine local features into global shapes.

Pattern recognition in tufted capuchin monkeys (Cebus apella): the role of the spatial organisation of stimulus parts.

We report four experiments aimed at characterising the role played by the encoding of the spatial relationship between stimulus parts in pattern recognition in capuchin monkeys, as assessed by a matching to sample task. The results of the first experiment, which were also reliably replicated at different stages in the course of the study, indicated that the simultaneous rotation and/or translation of the four parts into which the stimuli were divided, but not a global rotation of the entire stimulus, impaired matching performance in capuchin monkeys. Experiments two and three showed that matching performance was not impaired following similar manipulations of a subset of one, two or three parts. In experiment four, the same task was presented to human subjects. The same pattern of results emerged for humans and monkeys in trials where all the four stimulus parts were presented. However, the matching performance of humans was affected more than that of capuchin monkeys when only a subset of stimulus parts was featured in the task. These results support the conclusion that the matching performance of capuchin monkeys is affected by the rearrangement of stimulus parts and, as such it seems to rely on global properties of the stimulus such as the spatial relationships of the component parts. However, the remarkable ability of capuchin monkeys to identify a stimulus on the basis of a subset of parts suggests that the reliance on the global properties of the stimuli may not be pervasive as it is in humans.

Local advantage in the visual processing of hierarchical stimuli following manipulations of stimulus size and element numerosity in monkeys (Cebus apella).

Previous studies suggest that monkeys process local elements of hierarchical visual patterns more quickly and more accurately than they process the global shape. These results could be indicative of differences between relatively high visual functions of humans and non-human primates. It is, however, important to rule out that relatively low-level factors can explain these differences. We addressed this issue with two experiments carried out on capuchin monkeys (Cebus apella) using matching-to-sample tasks featuring hierarchical stimuli. The first experiment assessed whether manipulations of stimulus size can affect the local advantage so far observed in this New World monkey species. An overall local versus global advantage still emerges in capuchins, irrespectively of the amplitude of the visual angle subtended by the hierarchical shapes. Moreover, a local-to-global interference, indicative of a strong local advantage, was observed for the first time. In the second experiment, we manipulated size and numerosity of the local elements of hierarchical patterns, mimicking procedures that in human perception relegate the local elements to texture and enhance a global advantage. Our results show that in capuchin monkeys, a local advantage emerges clearly even when these procedures are used. These results are of interest since extensive neurophysiological research is carried out on non-human primate vision, often taking for granted a similarity of visual skills in human and non-human primates. These behavioural results show that this assumption is not always warranted and that more research is needed to clarify the differences in the processes involved in basic visual skills among primates.

A comparative analysis of global and local processing of hierarchical visual stimuli in young children (Homo sapiens) and monkeys (Cebus apella).

Results obtained with preschool children (Homo sapiens) were compared with results previously obtained from capuchin monkeys (Cebus apella) in matching-to-sample tasks featuring hierarchical visual stimuli. In Experiment 1, monkeys, in contrast with children, showed an advantage in matching the stimuli on the basis of their local features. These results were replicated in a 2nd experiment in which control trials enabled the authors to rule out that children used spurious cues to solve the matching task. In a 3rd experiment featuring conditions in which the density of the stimuli was manipulated, monkeys' accuracy in the processing of the global shape of the stimuli was negatively affected by the separation of the local elements, whereas children's performance was robust across testing conditions. Children's response latencies revealed a global precedence in the 2nd and 3rd experiments. These results show differences in the processing of hierarchical stimuli by humans and monkeys that emerge early during childhood.

Categorization of above and below spatial relations by tufted capuchin monkeys (Cebus apella).

Using a matching-to-sample procedure, the researchers investigated tufted capuchins' (Cebus apella) ability to form categorical representations of above and below spatial relations. In Experiment 1, 5 capuchins correctly matched bar-dot stimuli on the basis of the relative above and below location of their constituent elements. The monkeys showed a positive transfer of performance both when the bar-dot distance in the two comparison stimuli differed from that of the sample and when the actual location of the matching stimulus and the nonmatching stimulus on the apparatus was modified. In Experiment 2, the researchers systematically changed the shapes of the located object (the dot) or the reference object (the horizontal bar). These manipulations did not affect the monkeys' performance. Overall, the data suggest that capuchins can form abstract, conceptual-like representations for above and below spatial relations.

Detection of grouped and ungrouped parts in visual patterns by tufted capuchin monkeys (Cebus apella) and humans (Homo sapiens).

The authors investigated perceptual grouping in capuchin monkeys (Cebus apella) and humans (Homo sapiens). In Experiment 1, 6 monkeys received a visual pattern as the sample and had to identify the comparison stimulus featuring some of its parts. Performance was better for ungrouped parts than for grouped parts. In Experiment 2, the sample featured the parts, and the comparison stimuli, the complex figures: The advantage for ungrouped elements disappeared. In Experiment 3, in which new stimuli were introduced, the results of the previous experiments were replicated. In Experiment 4, 128 humans were presented with the same tasks and stimuli used with monkeys. Their accuracy was higher for grouped parts. Results suggest that human and nonhuman primates use different modes of analyzing multicomponent patterns.

Grasping behavior in tufted capuchin monkeys (Cebus apella): grip types and manual laterality for picking up a small food item.

This study investigates prehension in 20 tufted capuchins (Cebus apella) in a reaching task requiring individuals to grasp a small food item fixed to a tray. The aim was twofold: 1) to describe capuchins' grasping techniques in detail, focusing on digit movements and on different areas of contact between the grasping fingers; and 2) to assess the relationship between grip types and manual laterality in this species. Capuchins picked up small food items using a wide variety of grips. In particular, 16 precision grip variants and 4 power grip variants were identified. The most frequently used precision grip involved the distal lateral areas of the thumb and the index finger, while the most preferred kind of power grip involved the thumb and the palm, with the thumb being enclosed by the other fingers. Immature capuchins picked up small food items using power grips more often than precision grips, while adult individuals exhibited no significant preference for either grip type. The analysis performed on the time capuchins took to grasp the food and withdraw it from the tray hole revealed that 1) precision grips were as efficient as power grips; 2) for precision grips, the left hand was faster than the right hand; and 3) for power grips, both hands were equally quick. Hand preference analysis, based on the frequency for the use of either hand for grasping actions, revealed no significant hand bias at group level. Likewise, there was no significant relationship between grip type and hand preference.

Consumption of cherries lowers plasma urate in healthy women.

To assess the physiologic effects of cherry consumption, we measured plasma urate, antioxidant and inflammatory markers in 10 healthy women who consumed Bing sweet cherries. The women, age 22-40 y, consumed two servings (280 g) of cherries after an overnight fast. Blood and urine samples were taken before the cherry dose, and at 1.5, 3 and 5 h postdose. Plasma urate decreased 5 h postdose, mean +/- SEM = 183 +/- 15 micro mol/L compared with predose baseline of 214 +/- 13 micro mol/L (P < 0.05). Urinary urate increased postdose, with peak excretion of 350 +/- 33 micro mol/mmol creatinine 3 h postdose compared with 202 +/- 13 at baseline (P < 0.01). Plasma C-reactive protein (CRP) and nitric oxide (NO) concentrations had decreased marginally 3 h postdose (P < 0.1), whereas plasma albumin and tumor necrosis factor-alpha were unchanged. The vitamin C content of the cherries was solely as dehydroascorbic acid, but postdose increases in plasma ascorbic acid indicated that dehydroascorbic acid in fruits is bioavailable as vitamin C. The decrease in plasma urate after cherry consumption supports the reputed anti-gout efficacy of cherries. The trend toward decreased inflammatory indices (CRP and NO) adds to the in vitro evidence that compounds in cherries may inhibit inflammatory pathways.

Global and local processing of hierarchical visual stimuli in tufted capuchin monkeys (Cebus apella).

Capuchin monkeys' (Cebas apella) relative accuracy in the processing of the global shape or the local features of hierarchical visual stimuli was assessed. Three experiments are presented featuring manipulations of the arrangement and the density of the local elements of the stimuli. The results showed a clear advantage for local level processing in this species, which is robust under manipulations of the density of the local elements of the stimuli. By contrast the density of the component elements linearly affected accuracy in global processing. These findings, which support those from other studies in which a local superiority emerged in animals, challenge the generality of early claims concerning the adaptive value of global advantage in the processing of hierarchical visual patterns.