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At least 73 records · Page 4Linked to original sources
PubMed1990

Perception of the relative distances of nearby sound sources.

The pressure of a sound varies systematically with a listener's distance from a sound source, providing a useful cue for perceiving changes in the distance between a listener and a sound-producing object. The pressure-discrimination hypothesis predicts that thresholds for discriminating changes in distance are constrained by the underlying ability to discriminate the resulting changes in sound pressure--specifically, that the smallest discriminable change in distance should be about 5% of the reference distance. Previous studies reported thresholds of about 5% for reference distances greater than a few meters but surprisingly worse thresholds for closer reference distances. In the present study, thresholds at two close distances, 1 and 2 m, were within the 5% range predicted from the pressure-discrimination hypothesis. Moreover, thresholds were significantly worse in a control condition in which the pressure cue was removed. Results of previous studies were adjusted to take into account the possibility of conservative response tendencies by the subjects. These adjusted findings agree well with the results of the present study and the pressure-discrimination hypothesis. It is concluded that variations in sound pressure are very useful for perceiving changes in listener-source distances, even at close distances.

Adult↗
PubMed1991

Perceived depth scales with disparity gradient.

Perceived difference in depth between two adjacent stimuli decreases with increasing disparity gradient even if the disparity stays constant, ie when the stimuli approach each other along paths within fronto-parallel planes. This depth scaling effect is more pronounced with line stimuli than with two isolated points or two small symbols and is insignificant for easily discriminable symbols. The decrease in perceived depth is more pronounced for horizontal orientation than for oblique or vertical orientation. The ratio of perceived depth difference to displayed disparity difference also decreases when the distance between the stimuli increases at a constant gradient in depth. This is to say that we are more correct in our depth estimates for steep gradients in depth when the euclidean distance between the stimuli is short.

Attention↗
PubMed1990

"Smart" mechanisms emerging from cooperation and competition between modules.

Three sets of experiments are described. The first set concerns the detection of the 3-D possibility of shaded 2-D block patterns. The data indicate that the human perceptual system is able to do this above chance level, but in a specific and restricted way, which suggests the possibility of a module devoted to it. The second set concerns the determination of the 3-D orientation of coloured 2-D patterns. The data show that the human perceptual system uses physical constraints of colour mixing in doing this. Again, the mechanism seems to have characteristics suggesting modularity. The third set is about the detection of skewed symmetry in dot patterns. Skewed symmetry can be used as a source of information about the slant and tilt of a surface with bilateral symmetry present on it. Therefore, a module for recovering this information might exist. All these empirical data show that Fodor's criteria of modularity can be used to test hypotheses about visual mechanisms recovering 3-D information from 2-D inputs. But this does not imply that the results prove modularity and cannot be interpreted otherwise. As an exercise the same story about these experiments is told with the use of jargon from ecological realism and connectionist approaches. It is concluded that some of the approaches to some perceptual mechanisms are not as divergent as they might seem. The main theme underlying modular, connectionist, and ecological approaches is the avoidance of central intelligence agencies by the incorporation of physical constraints. Within this broad framework different questions can be asked and answers attempted that may depend on personal taste.

Adult↗
PubMed1989

Binocular depth from surfaces versus volumes.

Subjects were asked to compare the relative depths of two binocular targets embedded in different random dot stereogram backgrounds. The disparities of the background points were either randomized, corresponding to a scattering of points within a volume, or arranged according to a sawtooth (triangle-wave) disparity profile (i.e., a set of slanted planar surfaces separated by sharp depth discontinuities). When the targets were embedded in the random volume, their depths were perceived in accordance with their relative disparities. But when the target points were embedded in the sawtooth surfaces their depths were systematically misperceived in a manner predicted by the incorrect depth interpretation of the background points. Rather than seeing a sawtooth pattern, the background points resembled a staircase in depth, and the targets, which appeared embedded in different steps, were misjudged in depth accordingly. The effect suggests a distinction between the depth processing of isolated binocular features and those associated with continuous surfaces.

Attention↗
PubMed1990

Accuracy of judging time to arrival: effects of modality, trajectory, and gender.

Observers' accuracy in using time-to-arrival (Ta) information was examined in 4 experiments. The issues included use of visual vs. acoustic Ta information, use of acoustic Ta information by blind Ss, use of Ta information controlling for velocity, and effects of angle of approach and arrival time on judgment accuracy. Visual information was used more efficiently than audiovisual and auditory information. Blind Ss used acoustical approach information as accurately as sighted Ss used visual information. Radial, oblique, and transverse orientations were used to examine effects of approach trajectory. Radial events were underestimated, whereas the more accurate transverse approach was likely to be overestimated. Oblique angle events yielded intermediate accuracies implying a spatiotemporal anisotropy. Women underestimated Ta more than did men. Possible reasons for Ss' judgment accuracy, including linear vs. nonlinear optical changes and relation to spatial skills and experience, were discussed.

Adult↗
PubMed1991

Induced motion: isolation and dissociation of egocentric and vection-entrained components.

Induced motion (IM) is illusory motion of a stationary test target opposite to the direction of the real motion of the inducing stimulus. We define egocentric IM as an apparent motion of the test target relative to the observer, and vection-entrained IM as an apparent motion of a stationary object along with an apparent motion of the self (vection) induced by the same stimulus. These two forms of IM are often confounded, and tests for distinguishing between them have not been devised. We have devised such tests. Our test for egocentric IM relies on evidence that this form of IM is due mainly to a misregistration of eye movements when optokinetic nystagmus (OKN) is inhibited, and on evidence that OKN is evoked only by stimuli in the plane of convergence. Our test for vection-entrained IM relies on evidence that vection is evoked only by the more distant of two superimposed inducing stimuli. Thus we found egocentric IM to be induced without vection or vection-entrained IM when subjects converged on a foreground moving display with a stationary display in the background, and vection-entrained IM to be induced without egocentric IM when subjects converged on a stationary-foreground display with a moving display in the background. The two types of IM were evoked in opposite directions at the same time when subjects converged on a foreground moving display while a background display moved in the opposite direction. The two forms of IM showed no signs of interaction, and we conclude that they rely on independent motion mechanisms that operate within distinct frames of reference. A control experiment suggested that the depth adjacency effect in IM is determined by the depth adjacency of the inducing stimulus to convergence, not just to the test target.

Acceleration↗
PubMed1978

An intra-cultural investigation of susceptibility to 'perspective' and 'non-perspective' spatial illusions.

Conventional Müller-Lyer and modified Müller-Lyer (without 'perspective' cues) illusions were presented to two samples of children aged between eight and 19, matched in education, but living in 'carpentered' and 'uncarpentered' environments in Zambia. Traditional differences in susceptibility have been obtained with both the variations of the Müller-Lyer illusion. In view of the lack of perspective cues in one of these, it is concluded that the perspective theory as presented within the 'carpentered world hypothesis' is inadequate. Since these differences are intra-cultural, they also do not support the hypothesis which suggests that cross-cultural variations in illusion susceptibility are due to genetic factors--such as macular (or retinal) pigmentation.

Adolescent↗
PubMed1975

Effects of training on dynamic stereo acuity performancy by males and females.

Dynamic stereo acuity thresholds were obtained for 30 male and female Ss at speeds of rotation of 120 degrees/sec. after pretraining at either O degree, 60 degrees, or 120 degrees/sec. Under conditions of no pretraining females showed significantly larger discrimination errors than males. Pretraining, however, resulted in comparable threshold performance between males and females. Socio-cultural factors responsible for these differences are suggested.

Depth Perception↗
PubMed1991

Effect of feature similarity on illusory conjunctions.

In four experiments, we examined whether the phenomenon of illusory conjunctions is constrained by feature similarity. Specifically, are illusory conjunctions more likely to occur between items with similar features than between items with dissimilar features? Feature similarity was manipulated in two dimensions: color and shape. Experiment 1 demonstrated that more illusory conjunctions occur between items with similar colors than between items with dissimilar colors. A similar effect was found for letter similarity in Experiment 2. Experiments 3 and 4 demonstrated that the similarity effect is still obtained for illusory conjunctions even when identification of the relevant features is near perfect. These findings introduce a new constraint in the process of feature integration. Additional implications of the similarity constraint for theories of feature integration are discussed.

Attention↗
PubMed1990

Visual alleys as a function of instructions under informative and reduced conditions of viewing.

Three experiments were designed to explore parallel and distance alleys as a function of instructions (apparent and objective) under three different distance-cue conditions. The main findings were that (1) the alleys for the apparent instructions were positioned closer to the median plane than those for the objective instructions, (2) in an indoor setting, the parallel and distance alleys were not different under either the apparent or the objective instructions, and (3) in an outdoor setting, the parallel alley lay inside the distance alley under both the apparent and the objective instructions. On the basis of comparison with some of the previous alley studies, it is suggested that exact control of instructions will not produce great discrepancy between the parallel and the distance alleys that were constructed indoors.

Adult↗
PubMed1976

An investigation of the relationship between viewing condition and preference for true and modified linear perspective and adults.

In four experiments, pictures varying in degree of perspective convergence from linear to parallel were observed under the following conditions: at an arbitrary station point, at correct station points, and with unconstrained view. Adults were asked to rank the pictures from the most to least natural and realistic-looking picture or from the most to the least accurate drawing. Subjects nearly always chose the parallel perspective pictures as most preferred and the linear perspective pictures as least preferred. Intermediate degrees of convergence were ranked accordingly. Results were interpreted in light of an argument for a pictorial station poing independent of the correct center of projection for a picture. Since this station point was calculated to be at a distance at least 10 times as great as the object is large, its assumption for pictorial viewing was termed the "Zoom "effect.

Adult↗