Laterality effects in perceptual matching

Two experiments are reported in which Ss had to indicate whether pairs of simple geometric forms were “same” or “different.” In Experiment I the two forms were either both in the left visual hemifield or both in the right hemifield. Reaction times were unaffected by the locus of the stimuli. In Experiment 2, in addition to left and right pairs, there were pairs in which one of the stimuli was on the left and the other was on the right. Under these conditions, reaction times were faster for pairs totally on the left than for pairs totally on the right. The data support the notion that implicit scanning patterns are important in determining laterality differences. When such scanning is not involved and when simple nonverbal stimuli and responses are employed, laterality differences are eliminated.     

Laterality effects in the recognition of depth-rotated novel objects

The dissociable neural subsystems theory proposes that left-hemisphere (LH) performance is dominated by a viewpoint-invariant (VI) recognition subsystem, whereas right-hemisphere (RH) performance is dominated by a viewpoint-dependent (VD) subsystem (Marsolek, 1999). Studies supporting this theory have used familiar objects and, therefore, may have been confounded by characteristics beyond perceptual features. Experiment 1, a lateralized sequential-matching task with novel objects, showed VD recognition in both hemispheres. In Experiment 2, some participants learned semantic associations for four novel objects, whereas others were exposed to the novel objects without the semantic associations. Both groups later performed a depth-rotated lateralized sequential-matching task. The participants who had learned semantic associations showed greater VD performance in the RH than in the LH; however, the participants in the control group showed equivalent VD performance in both hemispheres. The results suggest that hemispheric differences in VD performance may be partially attributable to an LH advantage for semantic processing.     

Laterality effects in the processing of syllable structure.

Recent phonological research has shown that the syllable plays a major role in the phonology of German. The present study investigates laterality effects in the processing of syllable structure by means of dichotic presentation of German word pairs that differ in number of syllables, but that differ minimally in the phonemes they comprise (e.g., BREIT and BEREIT). Results showed a sex difference in laterality for the processing of the experimental stimuli, with a greater right-hemispheric lateralization in men and a more bilateral organization in women.     

Laterality effects with visual perception of

Using the paradigm denoting a contralateral relationship between visual field and brain hemisphere, laterality effects with music notation and dots were investigated. Two groups of readers of advanced piano music were selected, one good, one poor. Each group participated in two visual half-field experiments, one using random dot patterns and the other using musical chords. Significant opposite field effects were found for the two kinds of stimuli across reading groups, the left field for dots and the right field for chords. With dots, a significant sex effect emerged, with males superior to females across groups. The only significant group difference appeared in the chord experiment, in which the good group was superior. A practice effect also was found only with chords. Results suggest that the left hemisphere is more important for recognition of music notation than the right.     

Laterality and modality-specific effects of chronic pain

Previous investigations indicated that thresholds to nonpainful tactile stimuli were elevated in chronic-pain patients when compared with pain-free individuals (Seltzer & Seltzer, 1986; Seltzer et al., 1988). The present study attempted to determine whether thresholds to tactual and visual stimuli also were elevated by chronic pain. Furthermore, lateralization of the pain effect on tactile thresholds was assessed by obtaining thresholds from both left and right arms. A decrease in tactile sensitivity to nonpainful stimuli in chronic-pain patients was confirmed, but laterality of the effect was not demonstrated. Visual thresholds were not significantly affected by chronic pain. The data in the present study, taken together with other data, support the proposition that pain does not affect right hemispheric processes more than left hemispheric processes.     

Laterality effects in perceived spatial location of hallucination-like voices

Aydin and colleagues reported a reversal of physiological 'right-ear advantage' in a group of right-handed patients with schizophrenia, using an auditory acuity test. In schizophrenia, auditory hallucinations may appear to be spatially located inside or outside the patient's head. Here we show, using virtual acoustic space techniques, that normal right-handed subjects have a right-ear advantage for correctly locating the 'source' of hallucination-like voices as from either inside or outside the head. We propose a model for understanding lateralised, external hallucinations in schizophrenia based upon reversal of normal cortical asymmetry for auditory spatial processing.     

Laterality and modality-specific effects of chronic pain.

Previous investigations indicated that thresholds to nonpainful tactile stimuli were elevated in chronic-pain patients when compared with pain-free individuals (Seltzer & Seltzer, 1986; Seltzer et al., 1988). The present study attempted to determine whether thresholds to tactual and visual stimuli also were elevated by chronic pain. Furthermore, lateralization of the pain effect on tactile thresholds was assessed by obtaining thresholds from both left and right arms. A decrease in tactile sensitivity to nonpainful stimuli in chronic-pain patients was confirmed, but laterality of the effect was not demonstrated. Visual thresholds were not significantly affected by chronic pain. The data in the present study, taken together with other data, support the proposition that pain does not affect right hemispheric processes more than left hemispheric processes.     

Laterality effects in identification of caricatures and photographs of famous faces

Recent evidence suggests that memory representations of familiar faces may exaggerate distinctive information as do caricatures (G. Rhodes, S. Brennan, & S. Carey, Cognitive Psychology, 1987). Therefore caricatures should be effective representations of faces and should yield a right hemisphere processing advantage, as do photographs of faces. Photographs and caricatures of famous faces were presented to the left visual (LVF), the right visual field (RVF), and centrally (CVF), in a name-face verification task. There was a LVF (right hemisphere) advantage for both caricatures and photographs on name-face mismatches but no VF difference for matches. These results were true for both accuracy and reaction time. Processing strategy differences that may account for the difference between matches and mismatches are discussed. Performance was generally better for photographs than for caricatures, irrespective of visual field condition.     

Laterality effects in risk preference: A test of portfolio theory

A central assumption in portfolio theory of risk preference is that for games with expected value constant the preference ordering of an individual should exhibit a single peaked preference function. This assumption was tested by determining the level of stochastic transitivity satisfied by triples of pairwise preference proportions among eight gambles. In only a small percentage of cases were the predicted levels of stochastic transitivity not satisfied. It was concluded that the results provided strong support for portfolio theory.     

Laterality effects, levels of processing, and stimulus properties

Two hypotheses of hemispheric specialization are discussed. The first stresses the importance of the kind of processing to which the stimulus is subjected, and the second stresses the importance of the nature of the stimulus. To test these hypotheses, four experiments were carried out. In Experiment 1 verbal material was employed in a same-different classification task, and an overall right visual field superiority was found. Experiment 2, in which verbal stimuli were subjected to visuospatial transformations (i.e. mental rotations), yielded no laterality effect. In Experiment 3 geometrical figures were employed in a classification task similar to that of Experiment 1, and an overall left visual field superiority was found. In Experiment 4 both verbal and geometric stimuli were employed. The results showed a significant interaction between field of presentation and nature of the stimulus and no interaction between field of presentation and level of processing.     

A comparison of the effects of formal similarity among trigrams and among word triads

The central question of this report concerned the role of formal similarity in free recall of lists of trigrams and lists of three-letter word triads. Similarity was manipulated among trigrams by duplicating letters and among triads by duplicating words. An initial study showed that lists of 16 letters were learned more rapidly than a list of 16 three-letter words. Therefore, in the major experiment, the Ss were given all appropriate elements on test trials so that only associative learning was required. Increases in formal similarity caused decreases in rate of learning for both types of lists, and the mechanisms of the interference seemed to be the same for both types of lists, However, the learning of the trigram lists was more rapid than the learning of the triad lists, the difference being maximal with low similarity.     

Laterality differences and practice effects under central backward masking conditions

Two experiments were conducted to examine laterality differences and practice effects under various central backward masking conditions. Critical stimulus onset asynchrony (SOA) was determined for subjects on 3 consecutive days using single letters as target stimuli (TS) and a pattern masking stimulus (MS). There was a right visual field (RVF) advantage on Day 1 but no difference between the visual fields on following days. The decline in the RVF advantage appeared to be dependent upon prior experience with laterally located letters, to be independent of initial experience with a particular set of letters, and to be more pronounced for females than for males. In addition, large improvements in performance were found, particularly between the first and second testing sessions. These practice effects were discussed in terms of the possible development of strategies for enhancing TS features or attenuating MS features.     

Laterality effects in judgment of the identity and position of letters: A signal detection analysis

In two experiments subjects received 100 ms tachistoscopic presentations, either to left or right of fixation, of a rectangular matrix of 12 cells. On each trial three cells were filled, each with a different symbol drawn from a set of 12 letters and digits. In one (the “letter” experiment) subjects had to decide whether a particular letter (nominated at the end of the trial) had been one of the three presented. In a second (the “position” experiment) they had to decide whether a cell in the matrix (again nominated at the end of the trial) had been one of those that contained a symbol. Judgments were made on a four-point rating scale, and measures of sensitivity and response bias were calculated. In the letter experiment sensitivity was greater for presentations to right of fixation, and in the position experiment for those to left.     

Laterality of Champion Athletes

Certain experimental designs are based upon the assumption that performance level becomes stabilized after a prolonged period of practice. This assumption was tested by taking a long series of repeated measurements upon a single S for the performance of each of several constant tasks, each task being tested singly in a separate series of measurements. Results showed that after thousands of practice trials on a simple task S may still be learning or showing other sequential effects in performance. These effects may disappear on one day only to reappear on the next. Therefore it is extremely doubtful that “practice to an asymptote” should be regarded as either an efficient or an effective method of eliminating sequential effects from an experiment proper.     

Future Research Directions in Laterality

This paper considers the current conceptual state of research into neuropsychological laterality and considers some issues which might appropriately be considered for the forward development of the field. It considers the biological context which has been adopted for these studies and the psychological significance of performance asymmetries. A principal emphasis of the paper is the degree to which inferences, rather than direct methodological deductions, can be drawn from the research undertaken. The status of the dichotomies which have been proposed, the role of interhemispheric transfer, and stages of processing models are considered. The degree to which cerebral asymmetries may be inferred to reflect normal processes of the brain is questioned, and some prospects of the future discussed.     

Indices of Laterality in Turner Syndrome

The present study explored the utility of manual laterality in predicting verbal and visual-spatial functioning and educational placement among girls and adolescents with Turner syndrome (TS). A significant curvilinear relationship emerged between derived Performance Intelligence Quotient (PIQ) and motor skill laterality such that either very strong or very weak laterality was less advantageous for visual-spatial skills than moderate laterality. A significant negative correlation, but no curvilinear relation, emerged between derived Verbal Intelligence Quotient (VIQ) and degree of motor skill laterality, with more strongly lateralized participants showing lower verbal skills than weakly lateralized participants. Hand preference category showed no significant relationships with VIQ, PIQ, or educational placement.     

Pitch interactions in the perception of isolated musical triads

In previous work done in our laboratory, we have investigated the perceived pitch class of isolated musical triads. We have found that as the amount of musical training increased, listeners perceptions progress, from very confused percepts of pitch class, to analytic percepts corresponding to the pitch class of the highest note in the triad, and finally to synthetic percepts corresponding to the root note for the more harmonic triad types. In the present work, we used a pitch matching technique to determine the actual pitch, rather than merely the pitch class, perceived when listeners analytically "hear out" a particular note in a major triad. There was a strong tendency for the pitch of the analytically perceived note to be displaced by as much as 60 cents in the direction of the other notes in the triad. The magnitude of this effect decreased as musical training increased, and it was also affected by the relative salience of the individual triad notes. These results have implications for the mechanism of triad perception, and for claims regarding the harmonic equivalence of triad inversions.     

Laterality effects in processing tonal and atonal melodies with affective and nonaffective task instructions

Right-handed university subjects were presented with monaural melodies that either conformed to the rules of the Western tonal system (tonal melodies) or that systematically deviated from it (atonal melodies) while containing similar contours and pitch skips. Subjects were tested under two different task instructions. One group was requested to judge whether each melody sounded correct or not (the nonaffective task); the other group had to judge whether each melody sounded pleasant or not (the affective task). The nonaffective task was found to elicit essentially no ear difference. In contrast, the affective instruction induced opposite and reliable laterality effects, depending on the valence of the response. The pleasant responses were indicative of a left hemisphere predominance and the unpleasant responses of a right hemisphere predominance. The results are consistent with the claim that the left hemisphere is biased toward positive emotions and the right to negative emotions. Moreover, the results suggest that affective appreciation of melodies is dissociable from their nonaffective judgment.     

Laterality patterns in young fluent readers

Neuropsychological profiles of kindergarten children who were reading fluently with understanding were compared with those of both chronological age controls and reading level controls. Finger tapping, dichotic listening, and nonverbal intersensory tasks succeeded in differentiating the two kindergarten groups, but not the kindergarten readers and the older reading level controls. Correlations among the measures were significant only for the young fluent readers, with greater bilaterality of both fine motor and linguistic functions being associated with better intersensory skills, indicating qualitative differences in central nervous system organization. Neuropsychological predisposition to early acquisition of reading is suggested.