Perception of similarity and laterality effects in tactile shape recognition

Similarity judgements were made about pairs of shapes explored haptically with the hands moving in the same (congruent), or opposite direction. Scanning shapes using an opposite manual direction was slower and less accurate. These results enabled stimulus selection for a further experiment that examined laterality effects in the haptic modality. Pairs of shapes were explored and the presence/absence of a target shape indicated using a pedal switch. Males showed a right hand disadvantage, whereas females were equally accurate at recognising target shapes with either hand, and were equivalent to males' left hand recognition accuracy. Direction of hand movements (congruent vs opposite) and target type also interacted with sex. These interactions and the 1-2 sec longer decision time by females suggest sex differences in the use of cognitive strategies rather than in hemispheric specialization of function.     

Reliability of non-verbal laterality effects in the visual modality

The present experiment investigated the reliability and magnitude of laterality effects in a non-verbal task in the visual modality. The use of a bilateral discrimination task in which participants indicated whether a centrally presented probe stimulus matched either of the bilaterally presented targets was presumed to provide control over attention deployment. This led to the prediction that a reliable left visual field advantage (LVFA) would be obtained. A total of 40 right-handed undergraduate students completed the bilateral discrimination task twice in a test-retest design. Although relatively large test-retest correlations suggested that the laterality effect was quite reliable, a significant LVFA was obtained in the first testing session, and a right visual field advantage in the second one. This finding parallels results obtained in previous work with non-verbal tasks and supports the notion that practice affects the direction of laterality effects. The discussion examines alternative explanations with emphasis on practice effects and possible attentional factors. A possible shift in the bivariate distribution of laterality scores is used as a tentative explanation of the apparent contradiction between the high test-retest reliability and the shift in laterality with practice.     

Reliability of non-verbal laterality effects in the visual modality

The present experiment investigated the reliability and magnitude of laterality effects in a non-verbal task in the visual modality. The use of a bilateral discrimination task in which participants indicated whether a centrally presented probe stimulus matched either of the bilaterally presented targets was presumed to provide control over attention deployment. This led to the prediction that a reliable left visual field advantage (LVFA) would be obtained. A total of 40 right-handed undergraduate students completed the bilateral discrimination task twice in a test-retest design. Although relatively large test-retest correlations suggested that the laterality effect was quite reliable, a significant LVFA was obtained in the first testing session, and a right visual field advantage in the second one. This finding parallels results obtained in previous work with non-verbal tasks and supports the notion that practice affects the direction of laterality effects. The discussion examines alternative explanations with emphasis on practice effects and possible attentional factors. A possible shift in the bivariate distribution of laterality scores is used as a tentative explanation of the apparent contradiction between the high test-retest reliability and the shift in laterality with practice.     

Reliability and magnitude of visual laterality effects: the influence of attention

Two studies investigated the test-retest reliability of laterality effects in visual tasks. In each of the studies, 160 right-handed participants were tested. In Experiment 1, a lexical decision task was used under four testing conditions: no control of attention, fixation control, bilateral presentation with endogenous cue, and bilateral presentation with exogenous cue. In Experiment 2, the same four conditions were used in a letter-matching task in which participants had to indicate whether two letters in a different case had the same name. Results showed a significant right visual field advantage in the first testing session. However, this advantage was eliminated in the second session, suggesting that attention was not fully controlled by any of the procedures. In addition, the reliability of laterality effects was greater when control of attention was applied. The discussion focuses on the importance of controlling attention when assessing laterality by means of a visual task. Alternative explanations of the present findings are also considered.     

Misperceiving facial affect: effects of laterality and individual differences in susceptibility to visual hallucinations

It has been suggested that certain types of auditory hallucinations may be the by-product of a perceptual system that has evolved to be oversensitive to threat-related stimuli. People with schizophrenia and high schizotypes experience visual as well as auditory hallucinations, and have deficits in processing facial emotions. We sought to determine the relationship between visual hallucination proneness and the tendency to misattribute threat and non-threat related emotions to neutral faces. Participants completed a questionnaire assessing visual hallucination proneness (the Revised Visual Hallucination Scale - RVHS). High scoring individuals (N=64) were compared to low scoring individuals (N=72) on a novel emotion detection task. The high RVHS group made more false positive errors (ascribing emotions to neutral faces) than the low RVHS group, particularly when detecting threat-related emotions. All participants made more false positives when neutral faces were presented to the right visual field than to the left visual field. Our results support continuum models of visual hallucinatory experience in which tolerance for false positives is highest for potentially threatening emotional stimuli and suggest that lateral asymmetries in face processing extend to the misperception of facial emotion.     

Incidence of laterality effects in mandibular and manual performance of dichoptic visual pursuit tracking.

In dichotic pursuit auditory tracking tasks (PAT) subjects match a continuously varying pure tone presented to one ear with a second tone presented to the other ear and controlled by unidimensional movements of part of their motor system. In previous studies in which tonal frequency was varied, performance was significantly better when the tone controlled by a speech articulator (tongue, jaw) was presented to the right ear, rather than the left, but not if the tone was hand controlled. This study examined a visual analog of the PAT in which subjects matched the vertical position of a continually moving horizontal line (target) presented on one side of their point of fixation, with a second line (cursor) presented on the other side of their fixation point. Two predictions were confirmed for 12 right handed subjects: that there would be no significant laterality effect for articulatory (jaw) tracking because previous auditory tracking findings were speech related; and, that there would be a significant laterality effect (cursor right field-left hemisphere) for right hand tracking because of the development of a specialized sensorimotor integration mechanism for eye-right hand coordination in the left hemisphere. Alternative explanations for the right hand tracking results, and for the nonsignificant trend towards a laterality effect (cursor left field-right hemisphere) for left hand tracking, were discussed.     

Opposite brain laterality in analogous auditory and visual tests

Laterality for language processing can be assessed by auditory and visual tasks. Typically, a right ear/right visual half-field (VHF) advantage is observed, reflecting left-hemispheric lateralization for language. Historically, auditory tasks have shown more consistent and reliable results when compared to VHF tasks. While few studies have compared analogous tasks applied to both sensory modalities for the same participants, one such study by Voyer and Boudreau [(2003). Cross-modal correlation of auditory and visual language laterality tasks: a serendipitous finding. Brain Cogn, 53(2), 393–397] found opposite laterality for visual and auditory language tasks. We adapted an experimental paradigm based on a dichotic listening and VHF approach, and applied the combined language paradigm in two separate experiments, including fMRI in the second experiment to measure brain activation in addition to behavioural data. The first experiment showed a right-ear advantage for the auditory task, but a left half-field advantage for the visual task. The second experiment, confirmed the findings, with opposite laterality effects for the visual and auditory tasks. In conclusion, we replicate the finding by Voyer and Boudreau (2003) and support their interpretation that these visual and auditory language tasks measure different cognitive processes.     

Electrophysiological correlates of visual masking

The phenomenon of paracontrast documented by means of psychophysical techniques has not been readily demonstrable using electrophysiological responses as an index of masking. We have analyzed averaged cortical potentials during presentation of visual stimuli that produce psychophysical masking. Differences in the masking profiles obtained from the two experimental conditions are apparent. However, both electrophysiological and psychophysical data do indicate an interaction between responses to an annulus and a disc which varies with the time interval between the stimuli. Both sets of data also reflect differences in masking between right and left eyes. We conclude that the cortical potentials evoked by temporally disparate stimuli do interact, but that the masking profile is not identical to the profile obtained by psychophysical methods.     

Reliability and magnitude of visual laterality effects: further examination of the endogenous cueing procedure

The present study tests the hypothesis that laterality effects with bilateral displays would be larger and more reliable when lexically matched stimulus pairs are used rather than unmatched pairs. A total of 40 right-handed participants completed a lexical decision task using matched stimulus pairs in a bilateral display. These data were added to a previously collected set of data with 40 right-handed participants in which unmatched stimulus pairs were used. Results showed that the expected right visual field advantage (RVFA) was significant in words but not in non-words. In addition, a significant practice effect was found to be larger for matched than unmatched stimulus pairs. The predicted interaction between stimulus type, stimulus pairing, and visual field was not significant; contrary to the initial hypothesis, the RVFA was larger (though not significantly so) for unmatched displays than for matched ones. Finally, the laterality effect was found to be more reliable with unmatched than matched pairs in non-words, whereas no difference was found in words. The discussion emphasises the advantages of unmatched stimulus pairs and the conditions under which the bilateral effect is likely to emerge.     

The visual backward masking deficit in schizophrenia

1. Subjects with schizophrenia have an impairment very early in visual information processing, requiring a longer minimal stimulus duration than normal controls to identify a target stimulus. Subjects with schizophrenia have a deficit in visual backward masking, identifying fewer target stimuli than normal controls when the target is briefly obscured by a second visual stimulus When interstimulus interval is increased parametrically, subjects with schizophrenia have trouble identifying target stimuli at intervals that do not affect the performance of normal controls. 2. The visual backward masking deficit: is trait-related; is associated with negative symptoms but has also been associated with measures of thought disorder; may or may not be related to treatment with neuroleptic medication or other neurocognitive deficits of schizophrenia; is of unclear etiology, though researchers have speculated that it involves magnocellular channels and/or the cortical dorsal visual processing stream; has been shown to be heritable in one study. 3. If visual information processing deficits are observed in the unaffected siblings of schizophrenic patients, it may be a candidate intermediate phenotype.     

Response format,magnitude of laterality effects,and sex differences in laterality

The present study examined the evidence for the claim that response format might affect the magnitude of laterality effects by means of a meta-analysis. The analysis included the 396 effect sizes drawn from 266 studies retrieved by Voyer (1996) and relevant to the main effect of laterality and sex differences in laterality for verbal and non-verbal tasks in the auditory, tactile, and visual sensory modality. The response format used in specific studies was the only moderator variable of interest in the present analysis, resulting in four broad response categories (oral, written, computer, and pointing). A meta-analysis analogue to ANOVA showed no significant influence of response format on either the main effect of laterality or sex differences in laterality when all sensory modalities were combined. However, when modalities were considered separately, response format affected the main effect of laterality in the visual modality, with a clear advantage for written responses. Further pointed analyses revealed some specific differences among response formats. Results are discussed in terms of their implications for the measurement of laterality.     

Reliability and magnitude of visual laterality effects: Further examination of the endogenous cueing procedure

The present study tests the hypothesis that laterality effects with bilateral displays would be larger and more reliable when lexically matched stimulus pairs are used rather than unmatched pairs. A total of 40 right-handed participants completed a lexical decision task using matched stimulus pairs in a bilateral display. These data were added to a previously collected set of data with 40 right-handed participants in which unmatched stimulus pairs were used. Results showed that the expected right visual field advantage (RVFA) was significant in words but not in non-words. In addition, a significant practice effect was found to be larger for matched than unmatched stimulus pairs. The predicted interaction between stimulus type, stimulus pairing, and visual field was not significant; contrary to the initial hypothesis, the RVFA was larger (though not significantly so) for unmatched displays than for matched ones. Finally, the laterality effect was found to be more reliable with unmatched than matched pairs in non-words, whereas no difference was found in words. The discussion emphasises the advantages of unmatched stimulus pairs and the conditions under which the bilateral effect is likely to emerge.     

Response format, magnitude of laterality effects, and sex differences in laterality

The present study examined the evidence for the claim that response format might affect the magnitude of laterality effects by means of a meta-analysis. The analysis included the 396 effect sizes drawn from 266 studies retrieved by Voyer (1996) and relevant to the main effect of laterality and sex differences in laterality for verbal and non-verbal tasks in the auditory, tactile, and visual sensory modality. The response format used in specific studies was the only moderator variable of interest in the present analysis, resulting in four broad response categories (oral, written, computer, and pointing). A meta-analysis analogue to ANOVA showed no significant influence of response format on either the main effect of laterality or sex differences in laterality when all sensory modalities were combined. However, when modalities were considered separately, response format affected the main effect of laterality in the visual modality, with a clear advantage for written responses. Further pointed analyses revealed some specific differences among response formats. Results are discussed in terms of their implications for the measurement of laterality.     

Mental rotation and visual laterality in normal and reading disabled children

Normal and reading disabled children, aged from 11 to 13 years and matched for I.Q., were timed as they discriminated bs from ds. When the letters were presented only in their normal upright orientations, normal readers responded more quickly when they were presented in the right than in the left visual hemifield, while the disabled readers showed a slight but insignificant left hemifield advantage. When the letters were presented in varying angular orientations the reaction times indicated that both groups "mentally rotated" an internal representation of each letter to the upright in order to discriminate them. The two groups did not differ in the accuracy of discrimination or in the estimated rate of mental rotation, and there were no significant hemifield differences in this phase of the experiment. These data offer no support for the view that disabled readers are deficient in spatial ability, but confirm earlier evidence that they may suffer a lack of left-hemispheric specialization.     

Electrophysiological correlates of common-onset visual masking

In common-onset visual masking (COVM) the target and the mask come into view simultaneously. Masking occurs when the mask remains on the screen for longer after deletion of the target. Enns and Di Lollo [Enns, J. T., & Di Lollo, V. (2000). What's new in visual masking? Trends in Cognitive Sciences, 4(9), 345-352] have argued that this type of masking can be explained by re-entrant visual processing. In the present studies we used high-density event-related brain potentials (HD-ERP) to obtain neural evidence for re-entrant processing in COVM. In two experiments the participants' task was to indicate the presence or absence of a vertical bar situated at the lower part of a ring highlighted by the mask. The only difference between the experiments was the duration of the target: 13 and 40 ms for the first and second experiment respectively. Behavioral results were consistent between experiments: COVM was stronger as a joint function of a large set size and longer trailing mask duration. Electrophysiological data from both studies revealed modulation of a posterior P2 component around 220 ms post-stimulus onset associated with masking. Further, in the critical experimental condition we revealed a significant relation between the amplitude of the P2 and behavioural response accuracy. We hypothesize that this re-activation of early visual areas reflects re-entrant feedback from higher to lower visual areas, providing converging evidence for re-entrance as an explanation for COVM.     

Modulation of attention during visual masking in schizophrenia

OBJECTIVE: Schizophrenia patients consistently demonstrate performance deficits on visual masking procedures. The present study examined whether attentional manipulation would improve subjects' performance on visual masking. METHOD: A metacontrast task was administered to 105 schizophrenia patients and 52 healthy comparison subjects. Attention was manipulated by associating selected trials of the task with monetary reward. RESULTS: Schizophrenia patients exhibited poorer performance than the comparison subjects across conditions. Patients demonstrated modest, but statistically significant, improvement in performance with the attentional manipulation. This improvement was not significant for the comparison subjects. CONCLUSIONS: These findings suggest that early visual processes in schizophrenia are responsive to attentional manipulation but that the degree of improvement is relatively small, suggesting that these processes are not easily altered.     

Aiming in adults: sex and laterality effects

The purpose of the study was to twofold: to investigate gender-related differences in the asymmetry of aiming with the preferred and non-preferred hand in right-handed adults, and to examine the effect of the spatial requirements of the task on these asymmetries. The hypothesis was that if cognitive functions are more asymmetrically localised in men than in women, one should observe greater left-right differences on some variables in men than in women. Eleven men and eleven women were required to aim fast and accurately at one of three possible targets under a choice reaction time protocol. Performance and kinematics data were analysed. Results revealed an effect of target location on the left hand advantage in reaction time, and gender-related effects on movement time, accuracy, and on the velocity profiles. Overall, women performed more slowly and accurately than men. This gender-related effect could not be accounted for by differential strategies with regard to speed or accuracy, lending support to the idea that differences exist in the neural mechanisms of movement control between the two genders. Finally, although the results show a hand effect on terminal accuracy in men only, they do not support the hypothesis of a greater asymmetry of movement control in men.     

Offset masking in a divided visual field study

A problem in divided visual field studies (especially those using event-related potentials as a dependent measure) is the large number of horizontal eye movements participants make during experimental trials. Past attention research suggests that eye movements to lateralised targets should be significantly reduced using a dynamic, offset mask, causing a reduction in attentional capture. The current study attempted to replicate past divided visual field language studies using offset masking procedures. Using a basic offset procedure, eye movements were not reduced in Experiment 1. However, Experiment 2 did show a significant reduction in eye movements using a new dynamic offset masking procedure. Low accuracy rates were a concern throughout. In conclusion, horizontal eye movements can be reduced with a dynamic offset procedure but the low accuracy rates and the inconsistent behavioural findings throughout the study suggest that further study and refinement of the paradigm is needed.     

The effects of cross‐orientation masking on the visual gamma response in humans

Electrophysiological recordings in primates indicate that visual gamma contains distinct broad‐ and narrowband components that reflect different neuronal processes. Evidence suggests that cross‐orientation masking of luminance‐defined gratings should differentially modulate these two components. To test this we measured the effect of cross‐orientation masking on the gamma response in 12 human participants using magentoencephalography (MEG). Although both the amplitude and the frequency of gamma were modulated by the presence of a cross‐orientation mask, we failed to find evidence for distinguishable components: both broadband gamma at stimulus onset and sustained narrowband gamma were similarly modulated by mask contrast. However, we could not confirm the presence of masking effects due to mask contrast being confounded with the contrast of the stimulus as a whole. We therefore tested a further 12 participants in a second experiment in which the stimuli were: a plaid stimulus, the two component gratings which formed the plaid and the same two gratings but with Michelson contrast matched to the plaid. We found that gamma amplitude was reduced and gamma frequency increased to the plaid stimulus when compared with the contrast‐matched gratings or with the sum of the two component gratings, indicating that visual gamma was indeed modulated by cross‐orientation masking. Surprisingly, masking did not affect the pattern‐onset evoked response, challenging previous hypotheses that cross‐orientation suppression – the phenomenon by which the response to an orientated grating is suppressed by a cross‐orientation mask – is driven by feedforward inputs to V1.