Visual perception of surface curvature: psychophysics of curvature detection induced by motion parallax

The continuous approach to optic-flow processing shows that the curvature of a moving surface is related to a second spatial derivative of the velocity field, the spin variation (Droulez & Cornilleau-Pérès, 1989). With this approach as a theoretical framework, visual sensitivity to the curvature of a cylinder in motion was measured using a task of discrimination between cylindrical and planar patches. The results confirm the predictions suggested by the theory: (1) Sensitivity to curvature was always greater when the cylinder axis and the frontal translation were parallel than when they were orthogonal. The ratio of curvature detection thresholds in the two cases was between 1.3 and 2.5; the value predicted from the spin variation theory is about 2. (2) Sensitivity to curvature increased strongly with the velocity of the motion but was only weakly affected by its amplitude and the duration of viewing for the range of values used in our experiments.     

Apparent motion: evidence of the influence of shape, slant, and size on the correspondence process

Four stimulus elements configured as a notional diamond were flashed in pairs to elicit apparent motion. When the elements were identical (4 Zs), the direction of apparent motion was ambiguous. When the elements were pairs of different letters (Cs and Os, Es and Zs), letters of different sizes (Zs and zs), or oppositely oblique lines, the direction of apparent motion tended to be between identical elements. This was true, however, only for an initial, brief observation period. Subsequently, the direction of apparent motion tended to be determined by the direction of motion perceived at first, regardless of the character of the elements. This quickly established directional set (within 10 sec) largely swamped any tendency to resolve correspondence in terms of a feature of the stimulus. It appears to be based on spatial rather than retinal or egocentric coordinates.     

Semantic congruity effects in perceptual comparisons

Semantic congruity effects occur when, as in Experiment 1, for example, the time to select the shorter of two relatively short lines is faster than the time to select the longer; conversely, selection of the longer of two relatively long lines is faster than selection of the shorter. Semantic congruity effects are also demonstrated in experiments requiring comparisons of the heaviness of weights (Experiment 2) and horizontal extent (Experiment 3). In Experiment 1, the magnitude of the semantic congruity effect was larger under conditions emphasizing accuracy rather than speed and when the comparison was difficult. In fact, when comparisons were errorless, the effect was minimal (20 msec), thereby replicating previous failures to obtain the effect with supraliminal perceptual comparisons (Banks, Mermelstein, & Yu, 1982; Marschark & Paivio, 1981; Petrusic & Baranski, 1988a). In confirmation of Henmon's (1911) introspective analyses of psychophysical comparisons, Experiments 2 and 3 extend the range of the semantic congruity effect to include judgments of confidence. However, in each of the three experiments, semantic congruity effects were not evident with the response-accuracy measure. Finally, using highly confusable stimuli, in Experiment 3 the magnitude of the semantic congruity effect was shown to be larger for error than for correct response times. The implications of these findings for a decisional locus of the effect and for the semantic coding theory are discussed.     

Rate of processing and judgment of response speed: comparing the effects of alcohol and practice

Both alcohol and practice affect choice reaction time. The present study was conducted to investigate the possibility that impairment from alcohol and improvement with practice could be attributed to changes in the efficiency of control mechanisms (Rabbitt, 1979a), some of which depend upon the ability to judge response speed accurately. Twenty subjects participated in a four-choice reaction time experiment in which they received no alcohol (NA) in Session 1 and either no alcohol (10 subjects) or 0.8 ml alcohol (A) per kilogram of body weight (10 subjects) in Session 2. The task was to respond as fast and as accurately as possible to each stimulus. In addition, subjects were required to press a fifth key after any response that they considered to be both fast and accurate. Subjects had no difficulty in performing this task: (1) there was a significant difference of 122 msec between the mean response time for correct responses indicated as fast and that for correct responses not indicated as fast, and (2) subjects indicated 1 in 4 correct responses but only 1 in 64 errors. Alcohol increased all response times by approximately 40 msec. In contrast, practice decreased response times less for correct responses not indicated as fast than for correct responses indicated as fast. The ability to distinguish between fast and slow responses was thus unaffected by alcohol, but was improved by practice. Responses indicated as "fast" were significantly faster than errors, and appeared to occur without warning (unlike errors, which tended to end a sequence of increasingly fast correct responses). The results suggest that alcohol and practice influence choice reaction time in qualitatively different ways: Alcohol impairs overall response speed but has no effect on the ability to judge response speed, whereas practice improves both.     

Initial experiences with cognitive therapy of schizophrenic patients

Based on earlier experiences of various groups of authors, we developed and modified a programme of cognitive therapy for schizophrenic patients. The aim of the application of the therapeutic programme to subacute patients was to decrease subjectively perceptible basic disorders and to improve the functions of performance. The present results and experiences with 4 groups consisting of a total of 31 patients encourage us to continue applying cognitive procedures of therapy. Problems of the ascertainment of measuring values and fundamental questions of therapeutic efficacy are discussed.     

Association between paired subtests of auditory sequential memory administered to preschool children

Auditory sequential memory subtests of the Wechsler Preschool and Primary Scale of Intelligence and the McCarthy Scales of Children's Abilities were administered individually to 20 normal preschool children. Poor performance on the McCarthy words/sentences subtest suggests retention difficulties associated with isolated words in the absence of linguistic context. Correlations of only moderate strength and large unexplained variance indicate poor predictability between subtests despite similarities in content and procedural details.     

Peripheral apparent motion as a function of location, contrast, and direction of stimulus motion

This study investigated the perception of the direction of peripheral apparent motion as a function of stimulus location in the peripheral visual field, stimulus contrast, and the direction of the apparent motion. Results indicated that each of these independent variables was significant as a main effect while the interactions were not.     

Throwing action from full-cue and motion-only video-models of an arm movement sequence

The purpose of this study was to determine whether videotaped demonstrations of an action which displayed only the motion pattern of a model's limb as compared with one which showed both form and motion provide sufficient information for modelling a given pattern of movement. Video-demonstrations of an arm-movement sequence which ended with a throwing action were shown to adult subjects whose task was to model precisely what they saw. Each demonstration lasted 6 sec. and was shown 6 times. It portrayed the arm of a model, who held a small ball, performing a sequence of movements (flexion and extension of the elbow) which ended in the ball being thrown about 2.5 m with a 'darts-style' action. Three types of demonstration were presented: one showed the whole arm in dark clothing against a light-coloured background, another showed the arm as the relative motion of patches of light situated at the shoulder, elbow, and wrist joints, and the third showed the arm as the relative motion of the upper and lower segments of the arm represented by strips of light-reflectant material. These were the stimuli for the between-groups experimental conditions. Goniometry techniques were used to compare the performance of subjects relative to the model. Analysis showed that the order of the preparatory sequence was correctly produced after 4 trials under all conditions. Range of arm movement in projecting the ball closely approximated that of the model after 4 trials in all conditions. The time taken for the arm to project the ball remained constant across trials under all conditions and was always slower than the demonstrated cadence.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical applications of Rorschach-based visual imagery reactivity

A diverse set of findings from recent research suggests the value of visual imagery techniques in clinical practice.     

Effects of preshot routine on free-throw shooting

The effect of prohibiting the use of a preshot routine on free-throw shooting in competitive situations was investigated. 25 male high school basketball players were instructed to attempt 50 free throws alternating in blocks of 10 between the use of their preshot routine and shooting without it. To make the situation competitive, subjects were run in groups of five and their performance was recorded on a large easel placed to the side of the free-throw line. A significantly larger number of baskets were made in the preshot routine condition than without the routine. A competitive situation led to a greater decrement in baskets than had been reported in 1986 by Lobmeyer and Wassermen during noncompetitive free-throw shooting.