Visual depth discrimination in animals.

"The capacity to react discriminatively to the distance of visual stimulus appears to characterize a great many species, ranging from insects to primates. Especially in the case of insects, birds, and rats, it is evident that displacement of the images on the retinal mosaic is a very important factor in depth discrimination." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrast discrimination in human infants.

The ability to detect differences in spatial contrast is crucial to object recognition and identification. This ability is generally examined by measuring the contrast discrimination function. This function represents, for a variety of conditions, the smallest contrast difference required to discriminate otherwise identical patterns. We examined human infants' ability to discriminate patterns on the basis of differences in spatial contrast. The forced-choice preferential looking procedure was used to estimate contrast increment thresholds at a number of background contrasts. The Weber fractions of 6- and 12-week-old infants were about 1 log unit higher than adult values for background contrasts ranging from 0.14 to 0.55. Furthermore, the slopes of infants' discrimination functions were much shallower than those of adults. These age differences in contrast discrimination imply certain changes in the neural mechanisms that underlie contrast encoding. They also aid our understanding of the anomalies observed in early pattern vision. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling spatial integration and contrast invariance in visual pattern discrimination

PURPOSE: Human pattern discrimination performance has been reported to be largely independent of stimulus contrast but to depend on stimulus area. The authors propose a model that combines the effects of spatial integration and contrast. The model is based on the computation of similarity between pattern templates in memory and signals to be discriminated using normalized correlation. There are also two sources of additive noise, one before and one after the computation of correlation. The model was compared with human observers in an orientation discrimination task. METHODS: Orientation discrimination thresholds of human observers were measured for sinusoidal gratings of various areas, contrasts, and spatial frequencies. A two-interval, forced-choice methods was used. The performance of the model was determined by using computer simulations. RESULTS: It was found that the effects of contrast and grating area were interrelated. The decrease of orientation thresholds as a function of grating area was considerably larger at low than at high contrast. On the other hand, orientation thresholds decreased clearly as a function of contrast at the smallest grating areas but hardly at all at the largest grating areas. The model accounted well for the experimental findings. CONCLUSIONS: Because the invariance of orientation discrimination with respect to stimulus contrast depended on area, the cause of the invariance appeared to occur after spatial integration. The model explains this so that, with increasing contrast or area, the normalized correlation gradually approached a constant value. The proportion of pretemplate noise became negligible compared to the constant posttemplate noise. Thus, total noise also approached a constant value. Hence, the signal-to-noise ratio and discrimination performance became constant.     

Visual control of reaching and grasping in infants.

The role of visual input during reaching and grasping was evaluated. Groups of infants (5, 7, and 9 months old) and adults reached for an illuminated object that sometimes darkened during the reach. Behavioral and kinematic measures were assessed during transport and grasp. Both infants and adults could complete a reach and grasp to a darkened object. However, vision was used during the reach when the object remained visible. Infants contacted the object more often when it remained visible, though they had longer durations and more movement units. In contrast, adults reached faster and more precisely during transport and grasp when the object remained visible. Thus, continuous sight of the object was not necessary, but when it was available, infants used it for contacting the object whereas adults used it to reach and grasp more efficiently. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual following in newborns: role of figure-ground contrast and configurational detail

Visual pursuit was used in studying the ability of newborn infants to discriminate levels of contrast. Ratings of the degree of eye and head following were made as subjects pursued facial targets which varied in terms of the degree fo figure-gound contrast and te degree of contrast internal to the figure as defined by the presence of contrast such that the strongest pursuit occurred to stimuli which had clearly discriminable facial detailing in addition to strong figure-ground contrast. These results suggest that the newborn is sensitive not only to large border areas of high contrasting illumination but to finer configurational details of stimuli as well.     

Cardiac orienting and auditory discrimination in 6-wk-old infants.

A series of 3 experiments with 32 6-wk-old infants studied heart rate and sucking in response to changes in acoustic stimuli. Exp I used a conventional discrete trials paradigm to present trains of synthetic speech syllables, Exp II used a no-delay paradigm to present nonspeech stimuli (tone frequencies). Overall analysis of cardiac data indicated that discriminative capacities in 6-wk-olds can be revealed by changes in heart rate and that this discrimination is better demonstrated using a no-delay (rather than a discrete trials) paradigm. It is suggested that direction of this rate change may provide information about differences in processing, since cardiac responses to changes in synthetic speech syllables was accelerative (possibly a defensive or startle reaction) while responses to changes in tone frequency were decelerative (possibly an orienting index). Findings reveal a consistent absence of sucking responses, indicating that heart rate responses to changes in acoustic stimulation can occur independently of sucking in 6-wk-olds. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination in adult dairy bulls

Adult Holstein-Friesian dairy bulls were trained to recognize a black disk and then to discriminate between that disk and smaller ones. The bulls learned these tasks, but much more slowly than did dairy calves. Achievement of a consistently high percentage of correct choices varied among bulls because of daily variation in the disposition of the bull, which seemed to affect willingness to concentrate on the experimental task. Nevertheless, all bulls demonstrated learning, and each bull remembered very well what he once had learned. A 36-cm disk was easily detected and discriminated from smaller disks. However, bulls were not able to discriminate between two disks that differed in area by less than a factor of 4. The ability to use visual cues, such as shapes and size of shapes, suggested that the visual system is important in the biology of bulls. The slow learning rate and the variability in the percentages of correct responses were not considered to be an indication of cognitive disabilities in general but rather a reflection of the daily disposition of the bull, which affected his willingness to cooperate.     

Cognitive functioning in 8- to 18-month old drug-exposed infants.

This study examined the cognitive functioning in 236 infants at 8 and 18 months of age. Thirty-seven infants were heavily exposed to cocaine in-utero, 30 were lightly exposed, and 169 were not exposed to cocaine. Cognitive functioning was evaluated with the Bayley Scales of Infant Development (2nd ed.; N. Bayley, 1993) at both ages. Infant information processing was also assessed with an infant-controlled habituation procedure. Results indicated that (a) infants of cocaine-abusing women had higher neonatal medical and environmental risk scores; (b) at 8 months, exposure groups did not differ in Psychomotor Development Index, Mental Development Index (MDI) scores, or recovery to a novel stimulus; and (c) infants heavily exposed to cocaine or high environmental risk had a decrease in MDI scores from 8 to 18 months. These results were obtained when neonatal medical and environmental risk, as well as polydrug exposure, were controlled. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Color versus form discrimination learning in 1-year-old infants.

A comparison of form and color discrimination learning in 48 Ss showed that none of the color-trained Ss reached criterion, whereas approximately half of the form-trained Ss did reach criterion. Analysis showed that, in contrast to Ss who were given color problems, Ss who were given form problems showed both an initial curiosity about changes in form and an ability to solve form problems. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination defects in cats with temporal or occipital decortications.

Investigated performance on visual discrimination problems by 7 control (C) cats, 8 cats with lesions in the posterior temporal (PT) cortex, and 8 with destruction of the central 3-20° of the retina's projection to the marginal (M) gyrus. Group PT was impaired on 7/11 initial learning and transfer tests and on 0/3 retention tests with pattern stimuli and was inferior to Group C on 1/7 object discrimination tasks. No discrimination contingency was more likely than the others to reveal a significant deficit in Group PT. Group M was not impaired relative to Group C on any individual discrimination task. However, it made significantly more total errors on 7 discriminations between complex patterns (embedded or masked figures) than Group C. On 3 discriminations between simple patterns (unmasked figures), Group M made fewer errors than Group C. This pattern of loss is qualitatively similar to but milder than that observed in previous cats with M lesions, probably because the present M lesions were relatively small. Findings indicate that M and PT ablations produce differential impairments in cats, a selective difficulty in differentiating complex patterns after M lesions and a nonselective disruption of pattern discrimination learning after PT lesions. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual threat detection during moderate- and high-intensity exercise.

The aim of the study was to assess performance on a visual threat-detection task during concurrently performed vigorous exercise on a cycle ergometer. Thirty (15 female) participants completed a baseline condition of seated rest and then moderate- and high-intensity exercise. Moderate- and high-intensity exercise conditions were completed on the 2nd day in a counterbalanced order. During each exercise condition, participants responded to 3 × 3 picture matrices (256 trials in each condition) that contained discrepant fear-relevant and discrepant fear-irrelevant pictures (?hman, Flykt, & Esteves, 2001). Response accuracy was significantly greater, and reaction time was significantly faster, during moderate- and high-intensity exercise compared with the rest condition (ps     

Coherence thresholds for discrimination of motion direction in infants

The sensitivity of 3-month-old infants to direction of motion in random-dot patterns was assessed by measuring coherence thresholds for the discrimination of a pattern, in which opposite directions were segregated into alternate horizontal strips, from an unsegregated pattern. The coherently moving dots had a displacement size of 0.16 deg (velocity 8 deg/sec), and their direction of motion reversed periodically. For both infants and an adult subject coherence thresholds decreased with increasing height of the segregated strips, and with increasing duration of the interval between direction reversals. However the infants required larger minimum heights and longer minimum durations in order to extract motion direction. Even under the best conditions infants were markedly less sensitive, with coherence thresholds of around 50%, compared with 5-7% for the adult. In addition, within the group of infants coherence thresholds were negatively correlated with age. This developmental increase in motion sensitivity at an intermediate velocity suggests that a large part of the improvement in upper and lower velocity thresholds during development is a result of a uniform increase in sensitivity across all velocities, though the results do not rule out additional specific improvements in sensitivity at the extremes of the velocity range.     

Learning by selection: Visual search and object perception in young infants.

The authors examined how visual selection mechanisms may relate to developing cognitive functions in infancy. Twenty-two 3-month-old infants were tested in 2 tasks on the same day: perceptual completion and visual search. In the perceptual completion task, infants were habituated to a partly occluded moving rod and subsequently presented with unoccluded broken and complete rod test stimuli. In the visual search task, infants viewed displays in which single targets of varying levels of salience were cast among homogeneous static vertical distractors. Infants whose posthabituation preference indicated unity perception in the completion task provided evidence of a functional visual selective attention mechanism in the search task. The authors discuss the implications of the efficiency of attentional mechanisms for information processing and learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combining information: Probability summation and probability averaging in detection and discrimination.

Detection may improve if a stimulus offers 2 cues rather than 1. This is sometimes attributed to probability summation of independent detections, which provides an especially simple model for sensory information combination. However, this model assumes a strong bias toward the positive response, which is not appropriate for discrimination. The probability summation model is here extended to apply to discrimination and to allow different degrees of summation, ranging from complete through partial to probability averaging, and the use of this model is illustrated for the method of constant stimuli. It allows performance based on independent decisions to be distinguished from performance (e.g., integration) that is better than summation can explain. Models for the discrimination of complex stimuli may provide a tool for studying the development of expertise in areas where this involves a perceptual component, such as clinical judgment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination impairments in rhesus monkeys with combined lesions of superior colliculus and striate cortex.

To test the hypothesis that posterior inferotemporal cortex and the adjoining foveal prestriate cortex contribute to vision by combining inputs from striate cortex and superior colliculus, a total of 18 rhesus monkeys with combined collicular and partial striate lesions, foveal prestriate-posterior inferotemporal lesions, or subcortical lesions (controls) were tested in a series of visual discrimination tasks. Prestriate-inferotemporal lesions, unlike striate-collicular lesions, consistently impaired retention of a pattern discrimination and produced partial impairments in a size discrimination test. However, prestriate-inferotemporal and striate-collicular lesions produced similar deficits in pattern discrimination learning and no deficits in brightness discrimination learning. The deficits of the striate-collicular monkeys are discussed with regard to the "input-combining" hypothesis and alternative views. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual gap and offset discrimination and its relation to categorical identification in brief line-element displays.

Visual processing was investigated in judgments of relative line position. Stimulus continua were generated by bisecting a straight line and displacing the segments. Experiment 1 measured discrimination of pairs of longitudinally displaced segments at equal steps along the continuum. At long (2 s) durations discrimination fell smoothly, but at short (100 ms) durations it was sharp-peaked. In Experiment 2 the short-duration stimuli were labeled with subsets of the labels no gap, just a gap, and more than just a gap. Theoretical discrimination performances were computed and the one based on no gap and just a gap closely fitted observed performance. Experiments 3 and 4 were similar to 1 and 2, with lateral replacing longitudinal displacement. Similar "categorical" performance was obtained. It was concluded that there are discrete mechanisms for early detection of relative line position and that 2 labels can be used to characterize performance in each direction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)