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At least 289 records · Page 16Linked to original sources
PubMed1977

On the use of "calibration equations" in perception research.

Gogel's procedure of using "calibration equations" to obtain reports of perceived distance which are at least partially independent of individual differences in response bias, was examined. The procedure involves determining the relationship between reported and physical distances in a full-cue viewing situation. By making four assumptions, this equation can be used to "calibrate" responses gathered from other situations in which perceived distances are under investigation. In the present experiment, both verbal and string-pull measures of perceived distance were obtained for several objects under reduced viewing conditions. Calibration equations were determined for each response measure in a full-cue setting. The usefulness of the calibration technique was tested by comparing the differences between the two response measures for each object seen in reduced viewing, both before and after the application of the calibration procedure. The results indicated that, consistent with the usefulness of the calibration technique, group differences between the measures were almost always decreased by the procedure. However, no general improvement in the agreement of the measures was found when the data were examined on an individual basis. From the results, a modification of the method of calculating calibration equations was suggested that might increase its usefulness by simplifying the arithmetic operations required for the procedure.

Adolescent↗
PubMed1979

Spare the rod and spoil the icon.

Short-term visual storage was investigated with a successive field paradigm, so that correct performance depended upon combining visual information from two targets that were never on simultaneously. In the first two experiments, the stimuli consisted of two slides, each containing a 10' red dot on a gray surround, and separated by an interstimulus interval (ISI) from 20 to 400 msec. Subjects had to determine if the dots were vertically or horizontally aligned. In Experiment 1, the stimuli had either no contrast for the rods or no luminance contrast for the cones or high contrast. At short ISIs the cone contrast determined performance, whereas at long ISIs the rod contrast determined performance. In fact, when the dots were invisible to the rods, the task was impossible for long ISIs. In Experiment 2, performance was compared for zero log rod contrast and for small departures from zero. Even a small departure from zero log rod contrast resulted in above-chance performance. In Experiment 3, the stimuli were luminous rectangles and the task was to decide whether or not a 4' spatial gap was present between the two successively presented rectangles. Wavelength, luminance, and ISI were varied under both photopic and scotopic adapting conditions. The result was that the rods performed the task for ISIs of 150 msec or longer under scotopic conditions and under the photopic conditions that we were able to test. The results of the experiments taken together are consistent with the hypothesis that the cone icon is short, whereas the rod icon is robust and long lasting.

Color Perception↗
PubMed1990

Spatial, colour and contrast response characteristics of mechanisms which mediate discrimination of pattern orientation and magnification.

We have measured response times for the detection of a single target presented against a set of reference elements which are characterised by combinations of four different stimulus parameters; colour, contrast polarity, magnification and orientation. The aim of the experiments was to determine the response characteristics of visual mechanisms which mediate target detection through the discrimination of orientation and magnification. In the first experiments, we determined sensitivity to differences in colour and contrast polarity, and show that the mechanisms responsible for the discrimination of orientation and of magnification are both selective in their responses to colour and to contrast polarity. There are, nonetheless, residual interactions between patterns of different contrast polarities and between those of different colour, and in the latter case, weak interactions persist under equiluminance conditions. In a second set of experiments, we examined the interactions between orientation and magnification. We conclude that the responses of visual mechanisms which mediate target detection through discrimination of orientation are markedly dependent on stimulus magnification whereas those which mediate detection through discrimination of magnification are, in contrast, relatively insensitive to stimulus orientation.

Adult↗
PubMed1989

Manipulating stereopsis and vergence in an outdoor setting: moon, sky and horizon.

A simple stimulus generator has been constructed that permits a small illuminated target to be seen with variable inter-ocular disparity, when superimposed upon the binocular view of an outdoor landscape. This device was applied to several questions involving perception of size, distance and orientation, with the following results: (1) when the apparent distance to an "artificial moon", as perceived through stereopsis, is decreased by about 50-fold (from near horizon to about 60 m), its apparent size is reduced by only a miniscule amount (8% on average); hence, the moon illusion is probably not due to compensation--conscious or subconscious--for its apparent distance; (2) those changes in apparent size known as convergence micropsia vary as a function of the visual surround; for a vergence change of 1 deg, greater perceived change in size of a small target arises when a landscape is seen nearby than with empty sky as surround; (3) when a target is shown somewhat above the horizon against an empty sky, it must be viewed with divergence of the visual axes (image positions for "hyper-infinite" distance), in order to be perceived as vertically above objects on the skyline; this effect implies a strong backward tilt to the apparent vertical and probably reflects an attempt to "null out" the perceptual consequences of the convergence that typically occurs during downward saccades.

Depth Perception↗
PubMed1989

Length distortion of temporally extended visual displays: similarity to haptic spatial perception.

Three experiments were designed to investigate length distortion--the tendency to inflate estimates of the inferred distance between two points, as the length of a circuitous pathway between them increases. This phenomenon, previously demonstrated with haptic and locomotor exploration (Lederman, Klatzky, Collins, & Wardell, 1987), was extended to vision through the presentation of pathways as a temporal sequence of illuminated points. The magnitude of the visual effect was less than that previously found in haptics, and conditions promoting the effect included a relatively slow presentation rate and moderately complex pathways. Commonalities in the pattern, if not the magnitude, of length distortion in vision and haptics suggest that similar processes of spatial encoding may underlie the phenomenon in both domains.

Adult↗
PubMed1981

Assimilation and contrast in the parallel lines illusion?

Judgments of 40 undergraduates indicated that the assimilative character of the parallel lines illusion was destroyed at large values of both context line length and separation of context and center line variables. Accommodation of a portion of these results requires a modification of Brigner's (1977) theory of perception of illusory extent.

Discrimination Learning↗
PubMedDate not supplied

Some effects of prestimulus activity and length of prestimulus observation on judgments of newborns' responses to sounds.

Previous work on the effects of prestimulus state on newborn auditory response is briefly reviewed. Subjectively assessed responses of nine newborns by five observers were studied as a function of (1) prestimulus activity level and (2) duration of prestimulus observation period. Response assessment was significantly affected for the former but not by the latter. For sounds which elicited a high proportion of responses, the prestimulus activity level had relatively little effect on judgment of response, whereas for sounds (and no-sound "control" trials) to which few responses were ascribed, prestimulus activity tended to be associated with positive ratings of response.

Acoustic Stimulation↗