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Biomedical subjects

C Porac

Publications and source records attributed to C Porac.

At least 19 recordsLinked to original sources
PubMed1990

Overt attempts to change hand preference: a study of group and individual characteristics.

Previous work by Porac, Coren, and Searleman (1986) looked at overt attempts to change hand preference from the left to the right side. We extended this research by studying individuals who shifted their handedness from the left to the right side as well as a group who attempted a shift in the opposite direction (right to left). Comparisons of the two shift attempts revealed that the timing, method, and agent of change differed significantly for right versus left shifts. More right than left shifts were successful. Overall, most shift attempts were rated as unsuccessful because they did not result in a handedness classification consistent with the direction of the shift. Individuals classified as successful shifters, whether in the right or left direction, displayed a more ambihanded behavioural pattern than either unsuccessful shifters or the no shift control group. Evidence suggested that left-shift attempts were promoted by original ambihanded tendencies but that ambihandedness in successful right shifts stemmed from the partial success of the switch attempt.

Adult↗
PubMed1989

Relationship between birth order, birth stress, and lateral preferences: a critical review.

Reviews the literature examining the relationship between birth order, birth stress, and lateral preferences in nonclinical samples, with special emphasis on reports since 1971. The review found no evidence to relate birth order position to deviations from right-sidedness for either sex. More direct measures of birth stress indicated that deviations from right-handedness (particularly for male subjects), and also right-eyedness, were statistically related to specific birth stressors. It should be stressed, however, that all the relationships, including the significant ones, were very weak, accounting for less than 1% of the variance. When statistical significance was achieved, it was largely due to the huge sample sizes used in the meta-analyses. Methological and theoretical problems exist in the current literature, and we offer some suggestions to resolve them.

Birth Order↗
PubMed1989

Central and peripheral sensitivity to temporally modulated stimuli presented to the sighting and nonsighting eyes.

Thirty-two visually normal observers showed reduced sensitivity to uniform field flicker in the fovea of the nonsighting eye relative to the sighting eye. The two eyes showed equal sensitivity to flicker in the peripheral retina. This result with visually normal observers is analogous to that found in observers with functional amblyopia. It is also consistent with the hypothesis that amblyopic and normal suppressive processes share a common mechanism.

Contrast Sensitivity↗
PubMed1989

Is visual illusion decrement based on selective adaptation?

Illusion decrement is the reduction in the magnitude of visual geometric illusions with continued exposure, and it has been explained in two ways. The first explanation is the selective adaptation, or fatigue, of neural channels carrying orientation and/or spatial frequency information; the second explanation involves perceptual learning, in which the observer changes viewing strategy after continued exposure to a stimulus. Either mechanism could cause changes in the perception of a stimulus over time. One hundred twenty observers were tested in an illusion-decrement paradigm under exposure conditions that altered the amount of selective adaptation of specific neural channels. Observers were also measured on the magnitude of the transfer-of-decrement effect. Both decrement and transfer of decrement occurred, but there was no significant difference across exposure conditions. In addition, the pattern of transfer differed from that observed in selective adaptation paradigms. These results argue against a neural adaptation interpretation of illusion decrement.

Adaptation, Ocular↗
PubMed1986

Sighting dominance and egocentric localization.

Theories of the perception of visual direction use, either a hypothetical "projection center" midway between the two eyes, or the line of sight of the sighting dominant eye, as a reference point for egocentric localization. Seventy-five observers made judgments of the visual straight ahead. Their judgments varied as a function of both viewing condition and eye dominance. Judgments were biased toward the side of the viewing eye during monocular exposure, while binocular judgments were intermediate in their placement. Both monocular and binocular judgments were shifted in the direction of the sighting dominant eye, suggesting that the reference point for visual localization lies between the midpoint of the interocular axis and the line of sight of the sighting eye.

Depth Perception↗
PubMed1979

Normative data on hand position during writing.

It has been suggested that inverted versus upright handwriting position is an indicator of cerebral lateralization and the pattern of neuromotor control. Normative data on the prevalence of these handwriting positions was collected from 1758 subjects ranging in age from 10 to 75 years. Both age and sex differences in the prevalence of inverted handwriting positions were found.

Adolescent↗
PubMed1979

Heritability in visual-geometric illusions: a family study.

The Müller-Lyer and Ebbinghaus illusions were tested in 203 mother-father-offspring triads and 303 sibling pairs. Significant familial resemblances were found in all but the overestimated segment of the Ebbinghaus illusion. These results suggest that responses to visual-geometric illusions, mediated by optical or neural interactive mechanisms, show patterns of familial resemblance which may be based upon heritable factors.

Family↗
PubMed1979

Visual-geometric illusions: unisex phenomena.

The possibility of sex differences in responses to visual-geometric illusions was investigated with the use of forty-five illusion variants and a sample of 221 observers. No difference in illusion magnitude as a function of sex was found. A second experiment measured illusion decrement and transfer of decrement to other illusion configurations. Again there were no significant differences between male and female observers.

Female↗
PubMed1978

Iris pigmentation and visual-geometric illusions.

Blur or degrading of the retinal image has been shown to be a factor in the formation of visual-geometric illusions where intersecting line elements are present. Light irises allow more scattered light within the eye, which results in more image degradation than found in dark-eyed subjects. Measurements on 755 observers show that illusion magnitude varies as a function of iris pigmentation for a configuration with intersecting line elements (Müller-Lyer illusion), but not for a configuration devoid of such features (Ebbinghaus illusion).

Eye Color↗