Interhemispheric asymmetry in rats differentiating figures by size

Motor alimentary conditioned reflex was elaborated in Wistar line rats to presentation of various pairs of figures, those of larger area serving as positive signals. In tests on animals with intact brain and with unilateral hemispheric cortical inactivation, new pairs of figures were used besides basic stimuli. The level of analysis in testing experiment was lower than normal: by 5.6% at intact brain, by 16.4%--at right hemisphere inactivation, by 36.4%--at left hemisphere inactivation. Elimination of the left hemisphere produced prolongation of the conditioned reaction time, signs of frustration and aftereffect. In conditions of right hemisphere inactivation the level of discrimination of figures depended on their specific properties and the side of presentation. Conclusion is made on dominating role of the left hemisphere in analysis of abstract and concrete characteristics of visual stimuli, in control of temporal, spatial and emotional characteristics of reactions in situations when considerable abstraction and distinguishing of generalizing invariant sign "more-less" is necessary for elaboration of the conditioned reflex.     

Discrimination of a Right Angle with Monocular and Cyclopic Perception

Psychophysical tests with monocular and cyclopic perception were carried out to evaluate the accuracy of discrimination of right, acute, and obtuse angles. Tests with monocular perception were carried out with stimuli made by light line segments, spots, or elements of the Oppel-Kundt and Muller-Lyer figures. In tests with cyclopic perception, pairs of V-shaped stimuli with an identical orientation in the visual field and equal length of the sides but different divergence angles were presented to the different eyes of subjects. The test data demonstrated features of the perception of a right angle, namely, a high accuracy of reproduction, periodicity of errors as a function of the general orientation of a stimulus, similar characteristics of the manifestation of geometric illusions in angle reproduction and length comparison, and the manifestation of Hering’s law in cyclopic perception. These results agree with the multilocal hypothesis, which explains the perception of right and other angles on the basis of the information about the coordinates of stimulus parts.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 4, 2005, pp. 14–26.Original Russian Text Copyright © 2005 by Bulatov, Bertulis, Bulatova.     

Terrestrial chemical cues help coral reef fish larvae locate settlement habitat surrounding islands

Understanding the degree of connectivity between coastal and island landscapes and nearby coral reefs is vital to the integrated management of terrestrial and marine environments in the tropics. Coral reef fish are capable of navigating appropriate settlement habitats following their pelagic larval phase, but the mechanisms by which they do this are unclear. The importance of olfactory cues in settlement site selection has been demonstrated, and there is increasing evidence that chemical cues from terrestrial sources may be important for some species. Here, we test the olfactory preferences of eight island-associated coral reef fish recruits and one generalist species to discern the capacity for terrestrial cue recognition that may aid in settlement site selection. A series of pairwise choice experiments were used to evaluate the potential role that terrestrial, water-borne olfactory cues play in island-reef recognition. Olfactory stimuli tested included near-shore water, terrestrial rainforest leaf litter, and olfactory cues collected from different reef types (reefs surrounding vegetated islands, and reefs with no islands present). All eight island-associated species demonstrated high levels of olfactory discrimination and responded positively toward olfactory cues indicating the presence of a vegetated island. We hypothesize that although these fish use a suite of cues for settlement site recognition, one mechanism in locating their island/reef habitat is through the olfactory cues produced by vegetated islands. This research highlights the role terrestrial olfactory cues play in large-scale settlement site selection and suggests a high degree of ecosystem connectivity.     

Long-term Retention of Many Visual Patterns by Pigeons

Using a simultaneous discrimination procedure it was shown that pigeons were capable of learning to discriminate 100 different black and white visual patterns from a further 625 similar stimuli, where responses to the former were rewarded and responses to the latter were not rewarded. Tests in which novel stimuli replaced either the rewarded or nonrewarded stimuli showed that the pigeons had not only learned about the 100 positive stimuli but also about the 625 negative stimuli. The fact that novel stimuli enhanced discrimination performance when they replaced the many negative stimuli indicated that the pigeons had categorized the stimuli into two classes, familiar and less familiar. Long-term retention was examined after a 6-month interval. To begin with it seemed poor but a recognition test performed after the subjects had been retrained with a subset of the stimuli after an interval of 7 months confirmed that pigeons are capable of retaining in memory several 100 visual items over an extended period. It is proposed that the initial retrieval weakness was due to a forgetting of the contingencies between stimulus categories and response outcomes. Further tests involving variously modified stimuli indicated that while stimulus size variations had a negative effect on performance, orientation changes did not interfere with recognition, supporting the view that small visual stimuli are memorized by pigeons largely free of orientation labels. The experiment generally confirms that pigeons have the capacity of storing information about a large number of visual stimuli over long periods of time.     

Oscillatory neural network for pattern recognition: trajectory based classification and supervised learning

Computer algorithms that match human performance in recognizing written text or spoken conversation remain elusive. The reasons why the human brain far exceeds any existing recognition scheme to date in the ability to generalize and to extract invariant characteristics relevant to category matching are not clear. However, it has been postulated that the dynamic distribution of brain activity (spatiotemporal activation patterns) is the mechanism by which stimuli are encoded and matched to categories. This research focuses on supervised learning using a trajectory based distance metric for category discrimination in an oscillatory neural network model. Classification is accomplished using a trajectory based distance metric. Since the distance metric is differentiable, a supervised learning algorithm based on gradient descent is demonstrated. Classification of spatiotemporal frequency transitions and their relation to a priori assessed categories is shown along with the improved classification results after supervised training. The results indicate that this spatiotemporal representation of stimuli and the associated distance metric is useful for simple pattern recognition tasks and that supervised learning improves classification results.     

Hemispheric asymmetry of visual evoked potentials during human recognition of facial emotional expressions

Visual evoked potentials (VEP) in standard 16 EEG derivations were recorded in 26 young men and 20 women during recognition of facial emotional expressions and geometric figures. The stimuli were presented on a computer screen in the center of the visual field or randomly in the right or left vision hemifields. Peak VEP latency and mean amplitude in 50-ms epochs were measured; spatiotemporal VEP dynamics was analyzed in a series of topographic maps. The right hemisphere was shown to be more important in processing emotional faces. The character of the asymmetry was dynamic: at earlier stages of emotion processing the electrical activity was higher in the right inferior temporal region compared to the left symmetrical site. Later on the activity was higher in the right frontal and central areas. The dynamic mapping of "face-selective" component N180 of VEPs revealed the onset of activation over the right frontal areas that was followed by the fast activation of symmetrical left zones. Notably, this dynamics didn't correlate with the hemifield of stimuli exposition. The degree of asymmetry was lower during presentation of figures, especially in the inferior temporal and frontal regions. The prominent asymmetry of information processes in the inferior temporal and frontal areas was suggested to be specific for recognition of facial expression.     

Pulse-rate recognition in an insect: evidence of a role for oscillatory neurons

Various mechanisms have been proposed as the neural basis for pulse-rate recognition in insects and anurans, including models employing high- and low-pass filters, autocorrelation, and neural resonance. We used the katydid Tettigonia cantans to test these models by measuring female responsiveness on a walking compensator to stimuli varying in temporal pattern. Each model predicts secondary responses to certain stimuli other than the standard conspecific pulse rate. Females responded strongly to stimuli with a pulse-rate equal to half the standard rate, but not to stimuli with double the standard rate. When every second pulse or interval was varied in length, females responded only when the resulting stimuli were rhythmic with respect to the period of the standard signal. These results provide evidence rejecting the use of either high-/low-pass filter networks or autocorrelation mechanisms. We suggest that rate recognition in this species relies on the resonant properties of neurons involved in signal recognition. According to this model, signals with a pulse rate equal to the resonant frequency of the neurons stimulate the female to respond. The results are discussed with regard to both neural and evolutionary implications of resonance as a mechanism for signal recognition. In memory of Dagmar von Helversen (1944–2003)     

Compensation for disruptions of visual function in the dog after partial exclusion of the neocortex

The recovery of visual disturbances provoked by partial neocortical deafferentation was studied in dogs with two sets of visual patterns: figures and differently oriented lines. The disturbances were more prominent, when the dogs had to solve the most complex visual tasks (6 stimuli showed to a dog simultaneously). There was a distinct recovery of figure recognition in the process of compensation, i. e. in 4--6 months after the neocortical deafferentation. On the contrary, recognition of oriented lines did not improve. Probably the differences between the two sorts of recognition mentioned above may be explained by various changes of their mechanisms' properties in the process of compensation.     

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.     

Recognition of halftone and contour figures under their lateralization and masking

Recognition of shape of natural objects was studied during lateralized tachistoscopic presentation and different degree of noise-like ("rain drops") masking in 15 healthy subjects. Two sets of figures were used: halftone and contour ones. In all masking conditions, the mean group data showed a significantly better recognition of contour images by the left hemisphere as compared to the right hemisphere. The probability of correct response decreased with increase in the degree of masking. Contour figures were recognized significantly better than halftone figures. Gender differences in recognition were revealed. Male subjects displayed no hemispheric preference in recognition of both types of stimuli in both masking conditions. Possible neurophysiological mechanisms and functional significance of the findings are discussed.     

Effects of Acoustic Context on the Perceptual Differences between Spatial Sound Stimuli

We studied the effects of the acoustic context on active and passive discrimination of moving sound signals. Different contexts were created by reversing the role of standard and deviant stimuli in the oddball blocks, while their acoustical features were kept the same. Three types of sounds were used as standard or deviant stimuli in different blocks: stationary midline noises and two (smooth and abrupt) moving sounds moving to the left or right of the midline. Auditory event-related potentials (ERPs) were recorded during passive listening (the sound stimulation ignored), and mismatch negativity potentials (MMNs) were obtained. Active discrimination of sound movements was measured by the hit rate (percent correct responses) and false alarm rate, as well as the reaction time. The influence of the stimulus context on active and passive discrimination of the moving sound stimuli was reflected in the phenomenon known as the effect of deviance direction. The hit rate and MMN amplitude were higher when the deviant moved faster than the standard. The MMN amplitude was more responsive to the velocity of sound stimuli than the hit rate and false alarm rate. The psychophysical measurements in the reversed contexts suggest that smooth and abrupt sound movements may belong to the same perceptual category (moving sounds), while the stationary stimuli form another perceptual category.     

Size Estimates in Ebbinghaus Illusion in Adults and Children of Different Age

Psychophysical experiments were performed with the participation of 297 subjects (adults and 6- to 17-year-old children and adolescents). Perception of the size of a central stimulus surrounded by other stimuli was studied. Subjects had to estimate the size of a circle with a diameter of 22 angular min, which was surrounded by four similar figures with a diameter of either 11 or 44 angular min at a distance of either 11 or 33 angular min. The misperception of the stimulus size was dependent on the subject's age, the distance between the circles, and the size of the flanking circles. The smaller flanking circles located at any distance produced size underestimation in younger children; these circles led to size overestimation in case of their location at a short distance in most adults and adolescents. The larger flanking circles produced underestimation in all age groups, but, in adults, unlike children, this illusion decreased with increasing distance. The illusion mechanism and its possible connection with selective attention are discussed.     

COGNITIVE ASPECTS OF DIFFERENCE TESTING: MEMORY AND INTERSTIMULUS DELAY

There are many ways in which a laboratory difference test differs from 'real life' discrimination of foods. One of these is the interval of time between tasting the two stimuli to be discriminated. To investigate this, judges performed same-different discrimination tests using a citrus flavored beverage as a medium. The time interval between tasting the standard and comparison stimuli was varied. In this initial study, short intervals of zero, 30, 60 s were examined. For judges unfamiltar with the stimuli, performance deteriorated as the time interval increased. For judges familiar with the stimuli, the zero time interval elicited best performance but there was no decrease in performance when the interval was increased from 30 to 60 s. The results were explained by hypothesizing different types of memory trace for the standard stimulus being utilized for comparison with the comparison stimulus.     

Blocks and bodies: sex differences in a novel version of the Mental Rotations Test

A novel version of the Mental Rotations Test (MRT) that alternated the standard block figures with three-dimensional human figures was administered to 99 men and 129 women. Women and men differed predictably in their retrospective reports of childhood play and digit ratios, a putative measure of prenatal androgen action. Compared to the block figure items, human figure items on the modified MRT were associated with an improvement in performance in both sexes. However, consistent with the study hypothesis, the enhancing effect of the human figure condition on performance as measured by conventional scores was smaller in men compared to women and not at all evident in men when performance was measured by ratio scores. A closer inspection of the human figures effects on test scores showed performance in women improved for both male and female figure items. In contrast, relative to scores on block figure items, performance in men improved when stimuli were male figures but did not improve when stimuli were female figures. These results add to the evidence that the magnitude of sex differences in scores on the MRT may vary according to the test content and item properties. The findings suggest that online measures of cognitive processing in response to different classes of test stimuli (e.g., animate vs. inanimate objects, self-relevant vs. neutral stimuli) may prove useful in research aimed at understanding the hormonal and social factors contributing to the sex difference in performance on the MRT.     

Preferences for Call Spectral Properties in Hyla intermedia

We studied the pattern of variation in the spectral properties of male advertisement calls and female preference functions for these same properties in the Italian treefrog (Hyla intermedia). The call spectral properties (fundamental and dominant frequencies) were highly negatively correlated with body size, they showed low within‐individual variation, and, at the population level, they were found to be under weak stabilizing selection. In two‐choice discrimination tests, females did not show preferences between calls with fundamental and dominant frequencies within two standard deviations from the population mean, whereas females significantly discriminated against calls when their frequencies were three (or more) standard deviations above or below the population mean. Consistent with the observed permissiveness in female preference over the call spectral structure, in the natural population, we found no evidence either of directional selection on male body size or of a size‐assortative mating pattern. The pattern of preferences observed at the population level did not mirror the preferences of individual females. In fact, in a multi‐trial discrimination experiment, females showed significant differences in their choice between the average frequency call and a two standard deviation lower than average frequency alternative, for which no significant preferences were observed at the population level. Variations in preference were not found to correlate with female body size.     

Visual Ecology and Perception of Coloration Patterns by Domestic Chicks

This article suggests how we might understand the way potential predators see coloration patterns used in aposematism and visual mimicry. We start by briefly reviewing work on evolutionary function of eyes and neural mechanisms of vision. Often mechanisms used for achromatic vision are accurately modeled as adaptations for detection and recognition of the generality of optical stimuli, rather than specific stimuli such as biological signals. Colour vision is less well understood, but for photoreceptor spectral sensitivities of birds and hymenopterans there is no evidence for adaptations to species-specific stimuli, such as those of food or mates. Turning to experimental work, we investigate how achromatic and chromatic stimuli are used for object recognition by foraging domestic chicks (Gallus gallus). Chicks use chromatic and achromatic signals in different ways: discrimination of large targets uses (chromatic) colour differences, and chicks remember chromatic signals accurately. However, detection of small targets, and discrimination of visual textures requires achromatic contrast. The different roles of chromatic and achromatic information probably reflect their utility for object recognition in nature. Achromatic (intensity) variation exceeds chromatic variation, and hence is more informative about change in reflectance – for example, object borders, while chromatic signals yield more information about surface reflectance (object colour) under variable illumination. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism

Experimentation is at the heart of classical and modern behavioral ecology research. The manipulation of natural cues allows us to establish causation between aspects of the environment, both internal and external to organisms, and their effects on animals' behaviors. In recognition systems research, including the quest to understand the coevolution of sensory cues and decision rules underlying the rejection of foreign eggs by hosts of avian brood parasites, artificial stimuli have been used extensively, but not without controversy. In response to repeated criticism about the value of artificial stimuli, we describe four potential benefits of using them in egg recognition research, two each at the proximate and ultimate levels of analysis: (1) the standardization of stimuli for developmental studies and (2) the disassociation of correlated traits of egg phenotypes used for sensory discrimination, as well as (3) the estimation of the strength of selection on parasitic egg mimicry and (4) the establishment of the evolved limits of sensory and cognitive plasticity. We also highlight constraints of the artificial stimulus approach and provide a specific test of whether responses to artificial cues can accurately predict responses to natural cues. Artificial stimuli have a general value in ethological research beyond research in brood parasitism and may be especially critical in field studies involving the manipulation of a single parameter, where other, confounding variables are difficult or impossible to control experimentally or statistically.     

Haptic discrimination of size and texture in squirrel monkeys (Saimiri sciureus)

The present study analyzed haptic abilities of four squirrel monkeys. Using a two-alternative forced-choice procedure, stimuli were presented in a visually opaque box, allowing unrestrained test subjects to grab through a small opening and touch the discriminanda. Difference thresholds were determined by a modified method of limits. In the first experiment we determined size difference thresholds for the discrimination of circular cylinders using standard stimuli differing in diameter from 10 mm to 35 mm. In the second experiment a texture difference threshold was obtained for the discrimination of grooved surfaces (groove width 2-7 mm). The squirrel monkeys achieved a mean size difference threshold of 8% stimulus difference. The linear increase of absolute thresholds as a function of the starting stimulus size showed that haptic size discriminations in squirrel monkeys correspond to Weber's law. Three of the animals achieved a texture difference of 10% stimulus difference, while one monkey showed a distinctively lower haptic acuity. An analysis of the exploratory behavior points to a subject-related difference in the significance of cutaneous and kinesthetic information during size discriminations. Whereas differences in the animals' exploratory behavior did not correlate with the size difference threshold a subject achieved, different thresholds for texture discrimination can be explained by the different exploratory procedures the monkeys used to touch grooved surfaces. The low difference thresholds determined for the squirrel monkeys in the present study point to the significance of unrestrained test conditions for the assessment of the haptic capacity of a species.     

Haptic discrimination of size and texture in squirrel monkeys ( Saimiri sciureus )

The present study analyzed haptic abilities of four squirrel monkeys. Using a two-alternative forced-choice procedure, stimuli were presented in a visually opaque box, allowing unrestrained test subjects to grab through a small opening and touch the discriminanda. Difference thresholds were determined by a modified method of limits. In the first experiment we determined size difference thresholds for the discrimination of circular cylinders using standard stimuli differing in diameter from 10 mm to 35 mm. In the second experiment a texture difference threshold was obtained for the discrimination of grooved surfaces (groove width 2-7 mm).The squirrel monkeys achieved a mean size difference threshold of 8% stimulus difference. The linear increase of absolute thresholds as a function of the starting stimulus size showed that haptic size discriminations in squirrel monkeys correspond to Weber's law. Three of the animals achieved a texture difference of 10% stimulus difference, while one monkey showed a distinctively lower haptic acuity. An analysis of the exploratory behavior points to a subject-related difference in the significance of cutaneous and kinesthetic information during size discriminations. Whereas differences in the animals' exploratory behavior did not correlate with the size difference threshold a subject achieved, different thresholds for texture discrimination can be explained by the different exploratory procedures the monkeys used to touch grooved surfaces. The low difference thresholds determined for the squirrel monkeys in the present study point to the significance of unrestrained test conditions for the assessment of the haptic capacity of a species.     

Perceptual grouping of biological motion promotes binocular rivalry

Investigation of perceptual rivalry between conflicting stimuli presented one to each eye can further understanding of the neural underpinnings of conscious visual perception. During rivalry, visual awareness fluctuates between perceptions of the two stimuli. Here, we demonstrate that high-level perceptual grouping can promote rivalry between stimulus pairs that would otherwise be perceived as nonrivalrous. Perceptual grouping was generated with point-light walker stimuli that simulate human motion, visible only as lights placed on the joints. Although such walking figures are unrecognizable when stationary, recognition judgments as complex as gender and identity can accurately be made from animated displays, demonstrating the efficiency with which our visual system can group dynamic local signals into a globally coherent walking figure. We find that point-light walker stimuli presented one to each eye and in different colors and configurations results in strong rivalry. However, rivalry is minimal when the two walkers are split between the eyes or both presented to one eye. This pattern of results suggests that processing animated walker figures promotes rivalry between signals from the two eyes rather than between higher-level representations of the walkers. This leads us to hypothesize that awareness during binocular rivalry involves the integrated activity of high-level perceptual mechanisms in conjunction with lower-level ocular suppression modulated via cortical feedback.