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PubMed1977

Scalar perceptions of distance in simple binocular configurations.

Under reduced viewing, a single visual object tends to appear about 2 m away. Gogel (1972) found that the far point in a binocular configuration of two points of light also tended to appear about 2 m away, while the near point was displaced toward the observer. Attempts to replicate this latter result with points of light, as well as with a large rectangle for the nearer object, proved generally successful. Under some conditions, however, the far point was perceived to be closer to the observer when seen with the near point than when seen alone or with the rectangle. This unexpected result suggests caution in assuming that the far object in such a configuration will always remain at a stable perceived distance.

Distance Perception↗
PubMed1985

Retinal projection or size constancy as determinants of the horizontal-vertical illusion?

To compare the influence of the projected retinal size and of the figure size on the perception of the horizontal-vertical illusion, the target size, the viewing distance, and the slant of an illusion figure were varied. In the first experiment the illusion produced by two figures of the same object size but of different retinal size was compared with that of two figures projecting the same retinal size but differing in object size. The illusion diminished when the size of the retinal projection was increased, whereas a change in figure size did not change the illusion. In Exp. II the illusion figure was tilted backwards which reduced the retinal projection of the 'vertical' figure limb. The illusion decreased and became negative as a function of the retinal projection, but this decrease was relatively small compared with the reduction of the retinal image. The results are interpreted as supporting a retinal origin as an explanation of the illusion. Although there is strong evidence for size-constancy scaling in a tilted figure, constancy scaling is considered of minor importance as a determinant of the usual illusion.

Adolescent↗
PubMed1999

Is the anisotropy of perceived 3-D shape invariant across scale?

A number of studies have resulted in the finding of a 3-D perceptual anisotropy, whereby spatial intervals oriented in depth are perceived to be smaller than physically equal intervals in the frontoparallel plane. In this experiment, we examined whether this anisotropy is scale invariant. The stimuli were L shapes created by two rods placed flat on a level grassy field, with one rod defining a frontoparallel interval, and the other, a depth interval. Observers monocularly and binocularly viewed L shapes at two scales such that they were projectively equivalent under monocular viewing. Observers judged the aspect ratio (depth/width) of each shape. Judged aspect ratio indicated a perceptual anisotropy that was invariant with scale for monocular viewing, but not for binocular viewing. When perspective is kept constant, monocular viewing results in perceptual anisotropy that is invariant across these two scales and presumably across still larger scales. This scale invariance indicates that the perception of shape under these conditions is determined independently of the perception of size.

Adult↗
PubMed1989

The wide-angle pattern electroretinogram. Relation between pattern electroretinogram amplitude and stimulus area using large stimuli.

Pattern electroretinograms (PERGs) were recorded from two normal human subjects in response to various spatial frequencies and stimulus areas. The maximum stimulus area was 75 degrees x 86 degrees which was achieved by using a standard TV monitor and a reduced viewing distance. The amplitude of the PERG increased with area in an approximately logarithmic fashion over the range investigated. The explanation relates to non-linearities of the stimulus, the retinal image and neural processing. The wide-angle PERG may be useful in the assessment of retinal diseases affecting the mid-peripheral inner retina, such as diabetic retinopathy.

Electroretinography↗
PubMed1991

Responses to novelty in phobic and non-phobic cynomolgus monkeys: the role of subject characteristics and object features.

In two previous studies it has been shown that most surrogate-reared cynomolgus monkeys became phobic of a harmless object (a big paper bag) while most mother-reared monkeys approached that object. Results of the first study seemed to indicate that the phobic reaction was restricted to the bag. Barnett and Cowan (Interdisciplinary Science Review, 1, 43-62, 1976) and Suomi (Anxiety disorder in childhood, pp. 1-23, 1986), however, reported that subjects (respectively rats and monkeys) that avoided a first novel object also avoided subsequent novel objects. In the present study we exposed phobic (bag-avoiding) and non-phobic (bag-approaching) monkeys from the study by Röder, Timmermans and Vossen (Behaviour Research and Therapy, 27, 221-231, 1989) to several big and small novel objects. Our results show that, irrespective of their rearing conditions, subjects that were phobic also avoided big novel objects while subjects that were non-phobic approached big novel objects. The reaction to small novel objects was independent of the previous reaction to the bag.

Animals↗
PubMed1990

Developmental differences in visual processing: strategy versus structure.

The present study was an examination of two contrasting explanations for the finding that young children tend to classify objects according to similarity relations whereas adults emphasize dimensional structure. Subjects from three different age groups were given tasks that tapped different aspects of the visual process: Feature search, Conjunction search, and Restricted Classification tasks. In addition, three different stimulus objects (a highly separable, a highly integral, and an intermediate dimensional combination) were studied to explore the contribution of stimulus structure in dictating the nature of the processing mode. The results provided evidence against the view that children perceive objects according to a more primitive holistic structure. Rather, the results can be taken with past research to suggest that less efficient visual processing may lead the younger subjects to adopt a classification strategy that emphasizes similarity relations. In addition, the current research supported Garner's (1974, The processing of information and structure, Potomac, MD: Erlbaum) suggestion that the nature of the processing mode is stimulus-driven.

Attention↗
PubMed1994

Changes in the perceived direction of drifting plaids, induced by asymmetrical changes in the spatio-temporal structure of the underlying components.

When a plaid pattern with symmetrical velocity components (Type I) is changed to a plaid pattern with asymmetrical velocity components (Type IA), the overall direction of drift appears to undergo a rotation without any other change to the spatial parameters of the components. This change in the perceived drift direction can be induced by altering either the temporal frequency of the components or by altering their spatial frequency. In separate experiments, we have estimated the magnitude of the temporal and spatial frequency thresholds that are necessary to create a liminal change in direction of this type. The results from both temporal and spatial frequency experiments are closely similar. We find that liminal rotations can be induced by changes in the spatio-temporal structure of the sine-wave grating components that are undetectable when these components are presented in isolation. Further, we find that the "velocity threshold for direction" is not a constant factor, but critically depends on the relative orientation of the two elements that form the plaid. Forced-choice experiments were also conducted to estimate the extent of the apparent rotation of the plaid pattern for differing levels of asymmetry in the spatial frequency and temporal frequency of the components. The magnitude of the pattern rotation is predicted by a model of motion direction that encodes the successive displacements of the intersections of the gratings. Finally, we demonstrate that the velocity thresholds for perceived rotation exhibit a meridional anisotropy that depends on the direction of drift of the overall pattern and not on the orientation of the components.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1990

Nimodipine alters acquisition of a visual discrimination task in chicks.

Chicks 5 days old received intraperitoneal injections of nimodipine 30 min before training on either a visual discrimination task (0, 0.5, 1.0, or 5.0 mg/kg) or a test of separation-induced distress vocalizations (0, 0.5, or 2.5 mg/kg). Chicks receiving 1.0 mg/kg nimodipine made significantly fewer visual discrimination errors than vehicle controls by trials 41-60, but did not differ from controls 24 h later. Chicks in the 5 mg/kg group made significantly more errors when compared to controls both during acquisition of the task and during retention. Nimodipine did not alter separation-induced distress vocalizations at any of the doses tested, suggesting that nimodipine's effects on learning cannot be attributed to a reduction in separation distress. These data indicate that nimodipine's facilitation of learning in young subjects is dose dependent, but nimodipine failed to enhance retention.

Age Factors↗
PubMed2005

Task modulation of the effects of brightness on reaction time and response force.

Van der Molen and Keuss [van der Molen, M.W., Keuss, P.J.G., 1979. The relationship between reaction time and intensity in discrete auditory tasks. Quarterly Journal of Experimental Psychology 31, 95-102; van der Molen, M.W., Keuss, P.J.G., 1981. Response selection and the processing of auditory intensity. Quarterly Journal of Experimental Psychology 33, 177-184] showed that paradoxically long reaction times (RT) occur with extremely loud auditory stimuli when the task is difficult (e.g. needs a response choice). It was argued that this paradoxical behavior of RT is due to active suppression of response prompting to prevent false responses. In the present experiments, we demonstrated that such an effect can also occur for visual stimuli provided that they are large enough. Additionally, we showed that response force exerted by participants on response keys monotonically grew with intensity for large stimuli but was independent of intensity for small visual stimuli. Bearing in mind that only large stimuli are believed to be arousing this pattern of results supports the arousal interpretation of the negative effect of loud stimuli on RT given by van der Molen and Keuss.

Adult↗
PubMed2006

3D shape discrimination using relative disparity derivatives.

Three-dimensional (3D) shape discrimination could be achieved using relative disparity signals or it could be achieved using a higher-order disparity derivative detector. Two 3D shape discrimination tasks were used to distinguish between these possibilities: a within-shape task and a between-shape task. Disparity thresholds were larger when discriminating within the same shape than when discriminating between shapes. More importantly, within-shape discriminations were dependent on the pedestal disparity (distance from fixation) whereas between-shape discriminations were not. The results suggest that a mechanism sensitive to higher-order disparity derivatives can achieve discrimination between different 3D shapes.

Discrimination, Psychological↗
PubMed1991

Representation of spatial structure in reaching to a visual target.

Reaches made without feedback to positions on an object's surface reflect the spatial form of the surface. In Experiment 1, the reaching pattern varied with the stimulus surface's spatial attributes, consistent with a point-by-point perceptual representation of the surface. In Experiment 2, systematic reaching errors were determined solely by target position regardless of surface structure, implying a highly consistent representation of location. In Experiment 3, illusory slant was imparted to a surface by an aniseikonic lens. Individual variations in directly judged slant were reflected in the reaching pattern, implying organization of local perceptual representation of location and global perception of spatial attributes of the stimulus into a coherent structure.

Adult↗
PubMed1978

Normalization of irrelevant dimensions in stimulus comparisons.

When subjects compared two multidimensional stimuli with respect to a single (relevant) dimension in a same-different task, variation in the irrelevant dimension systematically affected reaction times. For same trials, reaction times increased monotonically with the amount of disparity between the stimuli on the irrelevant dimension. The dimensions were heights and widths of ellipses or hues and tints of color patches. The results were interpreted in terms of a normalization process that internally transforms the irrelevant dimensions of the two stimuli until they are equal. The amount of normalization, and hence same reaction time, increased with increasing disparity on the irrelevant dimension. These results suggest that in order to decide that two objects are equivalent in some criterial respect, it is often necessary to normalize irrelevant disparities.

Color Perception↗
PubMed1982

Loci of contextual effects in judgment.

Three experiments investigated the loci of contextual effects in judgment. Experiment 1 demonstrated the effect of stimulus spacing on category ratings and magnitude estimations of the darkness of dot patterns. Variations in the stimulus spacing were shown to affect both category ratings and magnitude estimations in a similar fashion. Experiment 2 was designed to determine whether contextual effects due to stimulus spacing influence the scale values or the judgment function. Subjects judged "differences" and "ratios" of the subjective darkness of dot patterns. Differences in mean judgments of single stimuli from Experiment 1 did not predict the rank order of judged "differences" and "ratios" from Experiment 2. The estimated scale values of the stimuli appeared to be independent of stimulus spacing. These findings suggest that contextual effects due to the stimulus spacing occur in the judgment function for within-modality judgments. Experiment 3 examined contextual effects in cross-modality judgments. Stimulus spacing and stimulus range were manipulated for "difference" and "total" judgments. Unlike the within-modality results, the stimulus range and spacing influenced the scale values. A contextual theory of within- and cross-modality judgment is presented.

Discrimination Learning↗