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Biomedical subjects

C Porac

Publications and source records attributed to C Porac.

At least 19 recordsLinked to original sources
PubMed2001

Lateral preference patterns as possible correlates of successfully switched left hand writing: data and a theory.

Left-handers often have had to contend with pressure to switch their preferred writing hand and shift attempt reports are common, especially among older adult left-handers. Three groups of left-handers can be defined by combining two variables, writing hand side and the report of a rightward hand preference shift attempt. The three groups are, first, right hand writers who report a rightward shift (successfully shifted left-handers); second, left hand writers who report a rightward shift attempt (unsuccessfully shifted left-handers); and, finally, left hand writers who do not report a rightward shift attempt. The underlying mechanisms that determine the success or failure of a handwriting shift attempt remain unclear. The present study examined the history of attempts to switch the preferred writing hand in a sample of 1277 adults aged 65 to 100 years of age. Older adults are well suited to participate in such a study because pressure to switch hand preference was especially severe for those who grew up in the early part of the 20th century; reports of rightward shift attempts are more common in this age group than among younger adults. Our results suggest that the three groups of left-handers, distinguished by the presence or absence of a shift history report and writing hand side, can also be distinguished from each other on the basis of their overall lateral preference profiles (the sides of hand, foot, eye, and ear preferences). Left hand writers, with and without reports of a rightward shift history, showed stronger left side lateralisation patterns when compared to right hand writers who reported a rightward switch (the successfully shifted left-handers).

Journal Article↗
PubMed2000

Hand preference side and its relation to hand preference switch history among old and oldest-old adults.

The last 10 years of research on adult hand preference patterns have generated a controversy over the meaning of the difference in the incidence rates of left- and right-hand preference in older adult samples (> 60 years old) when compared to samples of younger individuals (< 30 years old). Age differences in hand preference prevalence often are studied with large, cross-sectional age samples; however, with 1 notable exception (Gilbert & Wysocki, 1992), these large samples frequently are dominated numerically by individuals below the age of 45 years. This study reports on hand preference data from a sample of 1,277 individuals between the ages of 65 and 100 years. Overall, the participants in this sample displayed an incidence of 93.1% right preference versus 6.9% left preference. However, the occurrence of age differences in right-hand use when the oldest-old adults (> 73 years old) were compared to the others in this sample were only apparent for writing hand preference. Variation in hand preference prevalence was related to whether an individual reported a history of attempts to switch preference toward the right side. These findings support the view that age-related variations in hand preference prevalence are best explained by a number of factors, the interaction of which is still not well understood (Hugdahl, Satz, Mitrushina, & Miller, 1993; Hugdahl, Zaucha, Satz, Mitrushina, & Miller, 1996).

Adult↗
PubMed1999

Eye-dominance, writing hand, and throwing hand.

Handedness and eye-dominance are undoubtedly associated statistically, although a previous meta-analysis has found that the precise relationship is difficult to explain, with about 35% of right-handers and 57% of left-handers being left eye dominant. Of particular difficulty to genetic or other models is that the proportions are distributed asymmetrically around 50%. The present study asked whether this complicated pattern of association occurred because, following Peters, it is necessary to divide right-and left-handers into consistent handers (who write and throw with the same hand) and inconsistent handers (who write and throw with opposite hands). In an analysis of 10,635 subjects from questionnaire studies, 28.8% of left-handers and 1.6% of right-handers by writing were inconsistent for throwing. Our results also showed that writing hand and throwing hand both relate independently to eyedness, that throwing hand is somewhat more strongly associated with eyedness, and that the awkward asymmetry around 50% is now removed, 24.2% of consistent right-handers being left eye dominant compared with 72.3% of consistent left-handers, and 55.4% of inconsistent right-handers compared with 47.0% of inconsistent left-handers. We conclude that eyedness is phenotypically secondary to writing and throwing handedness. In our discussion we note that eyedness runs in families, we present new data suggesting that writing hand and throwing hand are co-inherited, and we argue that further data are now required to model properly the associations of writing hand, throwing hand, and eyedness, as well as probably also footedness and language dominance.

Journal Article↗
PubMed1997

Eye preference patterns among left-handed adults.

The sidedness congruency of limb (hand and foot) and eye preference was studied in a sample of 387 adults, ranging in age from 18-94 years. The sample contained approximately equal numbers of right- and left-handers. Results revealed that both right- and left-handers displayed a percentage incidence of congruency with eye preference that was greater than chance. In addition, the incidence of hand-eye congruency was higher among older adults. The odds of the occurrence of left eye preference were increased in the presence of either left hand or left foot preference in all of the age groups studied. The present findings are consistent with the results of a recent meta-analysis on the relationship between hand and eye preference conducted by Bourassa, McManus, and Bryden (1996); these results are also consistent with the idea of a common mechanism underlying limb and eye lateral preferences.

Journal Article↗
PubMed1996

Attempts to switch the writing hand: relationships to age and side of hand preference.

The recent suggestion that left-handedness is a mortality risk factor has prompted extensive media attention and has renewed research interest in generational differences in hand preference incidence and training. It is argued that differential generational training effects (the modification hypothesis), rather than decreased survival fitness (the elimination hypothesis), account for the lower numbers of individuals classified as left-handers in contemporary samples over the age of 60 years. A total of 633 individuals (aged 13-83 years) were queried about attempts to switch hand preference. Forty-one (6.5%) described efforts to shift preference in the rightward direction; of these, 21 (3.3%) reported attempted rightward writing hand shifts. The percentage of older adult left-handers, who reported right shifts in writing, was greater than the percentage of younger left-handers who described such attempts. Comparisons between the group reporting right shifts and those reporting no shift experiences suggested that the age-related decrease in leftward preference was specific to a decrease in the incidence of left-hand writing among older adults.

Journal Article↗
PubMed1995

Genetic vs. environmental contributions to human handedness: insights gained from studying individuals with unilateral hand injuries.

Four hundred eleven individuals who had suffered temporary unilateral hand injuries were assessed on five hand preference behaviors after their recovery. Measures of shifts to contralateral hand use experienced during and after the recovery period were taken. The best predictor of hand use shifts during the injury recovery period was whether the injury was to the preferred or nonpreferred hand. The incidence of postinjury contralateral shifts was low but was greater than that observed over a simulated injury period in a control group of 384 individuals who had not experienced a hand injury.

Adolescent↗
PubMed1994

Decrement and the illusions of the Mueller-Lyer figure.

Decrement, a time-related decrease in the magnitude of the Mueller-Lyer illusion, was measured separately for the wings-out and the wings-in variants of the Mueller-Lyer figure. There were significant reductions of wings-out illusion magnitude during the decrement period. Observers viewing the wings-in segment showed a non-significant decrement pattern. Analyses of individual decrement patterns showed that illusion magnitude did not decrease for a number of observers even when there were significant time-related trends at the group level. Data for 80 observers imply that the mechanisms of perceptual learning proposed by previous models of Mueller-Lyer illusion decrement are not sufficient explanations of the decrement process.

Adult↗
PubMed1993

Hand preference and the incidence of accidental unilateral hand injury.

Four hundred and eighty-six individuals gave detailed descriptions of an accidental unilateral hand injury and answered questions about their hand preference. Their handedness data were compared to 402 respondents (matched for sex and age) with no experience of hand injury. The risk of hand injury was similar for right- and left-handers. Individuals with consistent hand preference, regardless of side, were more likely to injure their preferred hand when compared to mixed preference types. The present data argue for a use explanation of hand injury risk (one is more likely to injure the hand that is used most frequently) rather than an explanation based on inherent risk factors present for left- but not for right-handers.

Accidents↗
PubMed1993

Are age trends in adult hand preference best explained by developmental shifts or generational differences?

Hand use in the performance of six everyday activities was analyzed as a function of age in a sample of 654 adults. An unskilled grasping tasks showed the largest shift toward consistent right-handedness as a function of age; skilled manipulation tasks, such as writing, exhibited weaker age-related trends. Analysis of individual preference patterns showed decreases in mixed right hand use (defined as a right-hander who occasionally uses the left hand) and increases in consistent right hand use in older adults. There was also a weaker age-related reduction in mixed left hand use but the numbers of consistent left-handers remained a small, constant percentage of the sample across all age groups. These results are congruent with the predictions of two developmental hypotheses offered to explain trends in adult hand preference. These are, first, a postulated age trend toward hand preference consistency and, second, a practice effect related to an environment arranged to favor right hand use.

Adolescent↗
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↗