Two experiments were conducted in which illusory and nonillusory figures were presented in the right and left tactual fields. Experiment 1 used 24 men (aged 18-24 years) and the Poggendorff'(P)illusion and an alignment (AI) task; Experiment 2 used another 24 men and the MullerLyer (ML) illusion and a line-match (Lm) task. Standard and mirror-image presentations of the figure were used in each case. Nested designs of analysis of variance and analysis of covariance were adopted for comparing left-and right-hand performance under each experimental condition. Covariance analysis on distortion scores of P and ML was performed separately with discrepancy measures on Al and Lm tasks as covariates. An investigation was also made into whether the direction of tactually perceived distortions was the same as or opposite to that reported for the visual illusions. The results show large P and ML tactual distortions. For ML, the tactual effects found were similar to those predictable from visual illusions, whereas for P, a high value ofinversion emerged. Differencesbetween hands were significant for P under the standard presentation, exploration with the right hand inducing a higher value of inversion. The latter results are discussed with reference to differences between the functions of human hemispheres which some authors have suggested for perceptual distortions.Susceptibility to visual illusions has been only marginally investigated in the context of functional hemispheric lateralization studies. As is well known, human hemisphere functioning is described in terms of contrasting modes of cognition, information processing, and coding (e.g., Bradshaw & Nettleton, 1981). According to the most current formulation, the left hemisphere may use analytic, serial, or sequential strategies, while the right uses global or parallel strategies (Simion & Bagnara, 1982); other studies point out the differences in coding information (Posner, 1978;Umilta, 1982). Friedman and Campbell-Polson (1981) proposed a model of the hemispheres as two independent and limited pools of resources, or subprocessors (Allen, 1983), which could be used in different ways. Whatever mechanism underlies the experimental data, however, there is general agreement that the left hemisphere is verbal, while the right is visuospatial. Basso, Bisiach, and Faglioni (1974) proposed that if illusions were due to perceptual distortion depending on structural features of a particular stimulus, right-hemisphere damage, by impairing the holistic attitude, should reduce susceptibility to the illusion, and left-hemisphere damage should enhance it. Basso et al. therefore studied performance in a linear-lengthdiscriminationtask and the extent of the Miiller-Lyer(ML) visual illusion in normal and unilateral-brain-damaged patients.Although linear-length discrimination was found to be impaired in right-brain-damaged patients with a visual field defect, Basso et al. found that, contrary to the hypothesis, left-brain-damaged patients showed reduced susceptibility to the ML. A seco...

No abstract

It is known from work by Helson and King that the apparent spatial distance between stimuli presented in succession depends on the time interval between those stimuli ("tau effect"). It is also known that the apparent time (i.e., the interval of time perceived between stimuli presented in succession) depends on the spatial distance between the stimuli defining the time interval (called "kappa effect" by Cohen, Hansel, and Sylvester). For the "kappa effect," apparent time between lights and stimuli on the skin of the forearm undergoes modification depending on the apparent spatial distance, as presented in Suto's work beginning in the early 1940s. The present work is complementary to Suto's. Its purpose is to test whether apparent spatial distance depends on the objective or subjective (apparent, phenomenal) time interval. To achieve this, our crucial (third) experiment was preceded by two exploratory experiments: the first to verify the illusion in which a subdivided interval appears longer than an empty interval of the same length (Oppel-Kundt temporal illusion); the second to verify the presence of the "tau effect" with simultaneous tactual and auditory stimuli for time intervals between 1500 and 2500 msec. In the third experiment subjects received successive tactual stimuli defining two spatial distance and two time intervals. They also received auditory stimuli that produced the Oppel-Kundt illusion by making the time intervals phenomenally different. The results fill a small experimental gap by showing it is subjective (phenomenal) and not objective (physical) time that influences perceived spatial distances.

The fingertips of right and left hand of normal subjects (right-handed male) were stimulated at random. After intervals of 0.3, 1.0, 3.0 and 6.0 seconds, an acoustic or tactile signal set off the response of the subject. The response was the ordered reproduction of the tactile sequence given to the subject. The results show a greater efficiency of right hand, a better recall of the first serial positions and of the last one but no difference depending on whether the recall signal is acoustic or tactile. The results are discussed and new hypotheses are formulated.