Verbal asymmetries and levels of processing in an interactive dual-task paradigm

This study examined how the dual-task laterality paradigm produces patterns of cerebral asymmetry different from those obtained in studies of comparable single-laterality tasks. We systematically examined at what level of processing a concurrent verbal memory-load influences accuracy of recognition of laterally presented nouns relative to that in a control condition. Four groups of 20 subjects each were tested in an interactive dual-task paradigm requiring them to compare lateralized nouns directly with one of three nouns concurrently held in memory prior to accuracy of recognition. The groups differed according to the types of comparisons being made: physical identity, phonetic orthographic similarity, phonetic similarity using non-orthographic words, and category membership. Subjects in each group carried out three tasks. They were required to determine if a specified match had occurred between a memory-load word and the lateralized word, identify the lateralized word, and report the memory-load words. Another 20 subjects were assigned to a control laterality condition in which no concurrent memory-load was used. Control subjects were required to respond to a laterally presented word by pressing a reaction-time key to indicate recognition of the word and then to report the word. No significant visual-field differences occurred in accuracy of recognition for either the control or matching-task groups. However, reaction-time latencies and errors increased as a function of the level of processing. The accuracy of recognition did not support the predictions of Kinsbourne's attentional model but the reaction times provided some support for the concept of selective left-hemisphere interference proposed by Hellige. A limited-capacity approach was suggested as a possible alternative explanation of laterality effects.     

Contrasting cases of Italian agrammatic aphasia without comprehension disorder

This study examined the effects of different concurrent verbal memory loads on a recognition accuracy task using bilaterally presented nouns. Four different memory load conditions were examined. They varied along a size dimension of either three or six words and along a complexity dimension of either easy concrete nouns or difficult highly abstract nouns. In each of the above conditions and in one control group, order or word report was controlled and in a second control group subjects were free to report the lateralized words in any order they wished. There were 20 subjects in each of the six groups. As expected, a significant right visual field superiority for verbal processing was obtained. there were no main effects of size of memory load nor complexity of m emory load on the laterality patterns. More subtle fluctuations in the patterns were found in the form of significant interactions between memory load, order of word report, and visual field. These interaction effects suggest that words reported second in the bilateral task, are more susceptible to the interfering effects of either larger or more complex memory loads. This is particularly true for right visual field words. While these data generally support a structural model of hemispheric organization, the interaction effects suggest that modifications must be made to the basic model to account for such factors as hemispheric capacity limits and order of report in the bilateral task.     

Absence of exposure time influence on lateralized face recognition and object naming latency tasks

J. Sergent (1982, Perception & Psychophysics, 31, 451-461; 1983, Psychological Bulletin, 93, 481-512) postulates that the left cerebral hemisphere preferentially extracts higher spatial frequency information, while the right hemisphere preferentially extracts lower frequency spatial information, from the visual scene. According to this view, shorter exposure times favor better right than left hemisphere performance, while longer exposure times favor better left than right hemisphere performance on tachistoscopic laterality tasks. We studied the effects of a threefold variation (40 msec versus 120 msec) in exposure duration, with constant 3-mL luminance, on face recognition and on object naming latency task performances. These are the same stimulus parameters employed by J. Sergent (1983, Psychological Bulletin, 93, 481-512) to demonstrate exposure duration effects in a task requiring the judgment of the sex of models from face photographs. We found the expected LVF superiority on the face recognition task and RVF superiority on the object naming task. There was, however, no influence of exposure duration on the performances. It is concluded that these tasks, which tap established lateralized processing asymmetries, are quite robust in their resistance to exposure time influence.     

Comparing visual perception on conventional cabinet tachistoscopes and computer monitor tachistoscopes

Computer monitor-based tachistoscopes (using a cathode ray tube, CRT) and conventional tachistoscopes differ in experimental control over stimulus continuity, duration, and timing accuracy. This study evaluated the perception of visual stimuli presented with the two different types of devices. An experiment was conducted to compare recognition of visuospatial stimuli (random shapes) presented laterally and centrally in the visual fields for short exposure durations (14, 29, and 43 msec), first with one device and then with another. Results indicated that the subjects’ error rates and laterality patterns were similar on both types of tachistoscopes. It was concluded that perception of visual stimuli presented as continuous images on a conventional tachistoscope may be equivalent to perception of visual stimuli presented as pulsating images on a CRT. Further studies are needed using other types of visual materials to determine the range of visual stimuli for which both types of tachistoscopes measure equivalent perceptual processes.     

Evidence that fixation digits can contribute to visual field asymmetries in lateralized tachistoscopic tasks

Fixation point digits have been widely used in tachistoscopic laterality studies as a simple and convenient means of ensuring unihemispheric projection of stimulus materials to the hemispheres. Previous findings demonstrate that fixation digits do not influence asymmetries in recognition accuracy studies with adult Ss. Present results, comparing four conditions differing in their use of fixation digits, show that in the naming latency paradigm the requirement to remember and report fixation control digits significantly augments RVF superiority. Implications for other latency tasks are discussed.     

Differential cerebral involvement in perceiving Chinese characters: levels of processing approach

Three experiments were designed to determine the accuracy and latency with which right-handed Chinese university students (12 females and 12 males) recognized Chinese characters in the left and right visual half-fields (VHFs). The experiments varied in the "depth" of processing required. Experiment 1 was a lexical decision task in which the configuration of the stimulus (a real Chinese character or the mirror image of a real character) determined whether the grapheme was an actual character. Experiment 2 required phonological processing; i.e., subjects had to decide whether a character (or a foil) matched the sound of an orally presented Chinese character. Experiment 3 required semantic processing; i.e., subjects had to decide if a character (or a foil) belonged to a particular semantic category. In each experiment, single characters were presented unilaterally for 150 msec. There was a significant right VHF superiority for accuracy scores for Experiments 2 and 3 but not for Experiment 1. None of the experiments yielded significant visual asymmetries in reaction time. The results do not support previous claims of orthography-specific laterality, but instead show that laterality effects for morphemic stimuli vary with the orthographic, phonological, and semantic processing demands of the task.     

Visual-field asymmetries in letter recognition: evidence for asymmetry in early visual registration

Two experiments on visual-field differences in tachistoscopic letter recognition are described. In the first, a bright pre-exposure field with a black fixation point was used, and the conventionally expected dominance of the right visual field was found. However, a large number of "blank" trials were observed, in which subjects completely failed to detect the presence of the flashed target. These "blanks" were themselves significantly asymmetric between visual fields, suggesting that asymmetry in early stimulus registration may play an unsuspected role in typical measures of cerebral asymmetry in recognition accuracy. This was confirmed in a second experiment in which use of dark pre-exposure fields eliminated "blanks" and led to higher over-all accuracy, with no visual-field differences. Implications for interpretation of laterality data with normal subjects are discussed.     

感知觉加工与概念加工对联结记忆中图片优势效应的影响

本研究采用联结再认范式考察联结记忆中感知觉水平和概念加工程度对图片优势效应的影响。实验1通过呈现清晰或模糊的词语或图片对操纵了感知觉水平,结果发现只有在清晰条件下图片优势效应才会出现;实验2则在模糊条件下通过要求被试想象两个项目之间的关系操纵了概念加工程度,结果发现在有概念加工条件下,出现了图片优势效应。研究结果表明：（1）降低的感知觉水平会导致联结记忆中的图片优势效应消失;（2）对模糊项目对进行概念加工会使联结记忆中出现图片优势效应。     

Recognition of affective and noncanonical linguistic facial expressions in hearing and deaf subjects

This study explores the use of two types of facial expressions, linguistic and affective, in a lateralized recognition accuracy test with hearing and deaf subjects. The linguistic expressions represent unfamiliar facial expression for the hearing subjects whereas they serve as meaningful linguistic emblems for deaf signers. Hearing subjects showed left visual field advantages for both types of signals while deaf subjects' visual field asymmetries were greatly influenced by the order of presentation. The results suggest that for hearing persons, the right hemisphere may predominate in the recognition of all forms of facial expression. For deaf signers, hemispheric specialization for the processing of facial signals may be influenced by the differences these signals serve in this population. The use of noncanonical facial signals in laterality paradigms is encouraged as it provides an additional avenue of exploration into the underlying determinants of hemispheric specialization for recognition of facial expression.     

Motivation, affect, and hemispheric asymmetry: power versus affiliation

In 4 experiments, the authors examined to what extent information related to different social needs (i.e., power vs. affiliation) is associated with hemispheric laterality. Response latencies to a lateralized dot-probe task following lateralized pictures or verbal labels that were associated with positive or negative episodes related to power, affiliation, or achievement revealed clear-cut laterality effects. These effects were a function of need content rather than of valence: Power-related stimuli were associated with right visual field (left hemisphere) superiority, whereas affiliation-related stimuli were associated with left visual field (right hemisphere) superiority. Additional results demonstrated that in contrast to power, affiliation primes were associated with better discrimination between coherent word triads (e.g., goat, pass, and green, all related to mountain) and noncoherent triads, a remote associate task known to activate areas of the right hemisphere.     

Investigating the anticipatory nature of pattern perception in sport

The aim of the present study was to examine the anticipatory nature of pattern perception in sport by using static and moving basketball patterns across three different display types. Participants of differing skill levels were included in order to determine whether the effects would be moderated by the knowledge and experience of the observer in the same manner reported previously for simple images. The results from a pattern recognition task showed that both expert and recreational participants were more likely to anticipate the next likely state of a pattern when it was presented as a moving video, but only the experts appeared to have the depth of understanding required to elicit the same anticipatory encoding for patterns presented as schematic images. The results extend those reported in previous research and provide further evidence of an anticipatory encoding in pattern perception for images containing complex, interrelated patterns.     

The influence of Hangul learning upon laterality differences in Hangul word recognition by native Japanese subjects

Single-character Hangul words were presented tachistoscopically in the left or right visual field to 34 normal, right-handed Japanese subjects who did not know Hangul. The reaction time was measured. A significant left-field superiority for Hangul recognition was shown. When 18 out of 34 subjects learned Hangul stimuli, they showed no lateral asymmetry for Hangul recognition. However, the other 16 subjects, without Hangul learning, again exhibited a significant left-field superiority. The results show that the initial left-field superiority shifted to no laterality difference for Hangul recognition by poor Hangul learners.     

Functionally lateralised information processing and its allocation to response: Inferences from three measures of letter identification performance following lateralised visual input

Identification errors were analysed for single letters presented in each visual hemi-field. The kinds of errors occurring reflected both how the letters were made difficult to see, and the informational relationships among the possible stimulus letters. The particular pattern of errors was different in the two hemifields, with the direction of that difference suggesting the letters were better differentiated following left half-brain input. But this left-sided superiority in letter differentiation was only sometimes reflected in faster or more accurate responses overall. Instead, the extent of left-sided performance superiority in RT and accuracy depended in a complex way on the degree of difficulty of the task. This influence of task difficulty on the RT and accuracy measures of functional laterality was considered to reflect a greater or lesser allocation to response of the lateralised letter-differentiation process revealed by the errors analysis.     

The lateralization of lip-read sounds: a first look

Two tachistoscopic studies on the lateralization of lip-read still photographs in normal right handers are reported. In the first, subjects matched a still lip photograph with a heard speech sound. A clear right hemisphere (LVF) advantage emerged, despite the phonological requirements of this task. This pattern of laterality failed to interact with the type of response (same/different) or with the status of the heard phoneme; both consonant and vowel matching showed the same pattern of LVF advantage, despite the significantly greater difficulty of consonant than vowel matching in this particular task. In the second study subjects were required to speak the sound they saw being spoken by a centrally displayed face photograph. The displayed face was chimeric; that is, one side of the face was seen saying one sound, one side another. Here, a rather complex pattern of results ensued. For the speakers seen a clear expressor asymmetry emerged; speech sounds were judged more accurately when they issued from the right side of the speaker's face. However, in the LVF, and only the LFV, accuracy in reporting chimeric face sounds correlated with speed in learning to lip-read, suggesting that the LVF is systematically involved even when task demands (speaking the response, phonological analysis, small, more central displays) do not, at first sight, suggest that they should. Taken together, these studies suggest that the right hemisphere could support some aspects of the processing of seen speech in normally hearing, normally lateralized individuals.     

Visual laterality responses to different emotive stimuli by red-capped mangabeys, Cercocebus torquatus torquatus

Hemispheric asymmetry in emotional perception has been put forward by different theories as the right hemisphere theory or the valence theory. But no consensus was found about the role played by both hemispheres. So, in order to test the different theories, we investigated preferential use of one eye in red-capped mangabeys, at the individual as well as at the group level. In this study we investigated the influence of the emotional value of stimuli on the direction and strength of visual preference of 14 red-capped mangabeys. Temporal stability of the bias of use of a given eye was evaluated by comparing our current results to those obtained 2.5 months previously. Two experimental devices, a tube and a box, tested five different stimuli: four food types varying in palatability and a neutral stimulus. The subjects’ food preferences were evaluated before testing the laterality. The mangabeys used their left eyes predominantly at the group level for the tube task. The majority of the subjects showed a visual preference at the individual level for the box task, but this bias was not present at the group level. As the palatability of the stimuli increased, the number of lateralized subjects and the number of subjects using preferentially their left eye increased. Similarly, the strength of laterality was related to food preference. Strength of laterality was significantly higher for subjects using their left eye than for subjects using their right eye. Preferential use of a given eye was stable over short periods 2.5 months later. Our data agree with reports on visual laterality for other species. Our results support the valence theory of a hemispheric sharing of control of emotions in relation to their emotional value.     

Visual laterality patterns for pure- versus mixed-list presentation

In Experiment 1, an overall left visual field advantage for nonverbal form recognition was found in a pure list of forms, but an overall right visual field form recognition advantage was found when the form trials were randomly intermixed with word recognition trials. Form complexity also influenced the form recognition laterality pattern, but the complexity effects were independent of (i.e., additive with) those produced by randomly mixing forms with words. Experiment 2 found that the mixed-list laterality pattern was unchanged by a pretrial cue indicating whether a word or form would follow. Experiments 3 and 4 demonstrated that holding two nouns in memory on each trial in a pure list of forms has much the same effect on laterality pattern as mixing forms with words but that the combined effect of these two variables is no larger than the effect of either variable alone. The entire pattern of results suggests that (a) laterality patterns are caused by the interaction of several factors, (b) the effects of random mixing and concurrent verbal memory are both caused by selective left-hemisphere activation, and (c) the form-complexity effects are caused by some other mechanism--perhaps subtle difference in stimulus codability.     

Functional lateralization, interhemispheric transfer and position bias in serial reversal learning in pigeons (Columba livia)

In the present study we investigated lateralization of color reversal learning in pigeons. After monocular acquisition of a simple color discrimination with either the left or right eye, birds were tested in a serial reversal procedure. While there was only a slight and non-significant difference in choice accuracy during original color discrimination, a stable superiority of birds using the right eye emerged in serial reversals. Both groups showed a characteristic ‘learning-to-learn’ effect, but right-eyed subjects improved faster and reached a lower asymptotic error rate. Subsequent testing for interocular transfer demonstrated a difference between pre- and post-shift choice accuracy in pigeons switching from right to left eye but not vice versa. This can be accounted for by differences in maximum performance using either the left or right eye along with an equally efficient but incomplete interocular transfer in both directions. Detailed analysis of the birds’ response patterns during serial reversals revealed a preference for the right of two response keys in both groups. This bias was most pronounced at the beginning of a session. It decreased within sessions, but became more pronounced in late reversals, thus indicating a successful strategy for mastering the serial reversal task. Interocular transfer of response patterns revealed an unexpected asymmetry. Birds switching from right to left eye continued to prefer the right side, whereas pigeons shifting from left to right eye were now biased towards the left side. The results suggest that lateralized performance during reversal learning in pigeons rests on a complex interplay of learning about individual stimuli, stimulus dimensions, and lateralized response strategies. Received: 4 June 1999 / Accepted after revision: 18 August 1999     

Valence-specific laterality effects in vocal emotion: interactions with stimulus type, blocking and sex

Valence-specific laterality effects have been frequently obtained in facial emotion perception but not in vocal emotion perception. We report a dichotic listening study further examining whether valence-specific laterality effects generalise to vocal emotions. Based on previous literature, we tested whether valence-specific laterality effects were dependent on blocked presentation of the emotion conditions, on the naturalness of the emotional stimuli, or on listener sex. We presented happy and sad sentences, paired with neutral counterparts, dichotically in an emotion localisation task, with vocal stimuli being preceded by verbal labels indicating target emotions. The measure was accuracy. When stimuli of the same emotion were presented as a block, a valence-specific laterality effect was demonstrated, but only in original stimuli and not morphed stimuli. There was a separate interaction with listener sex. We interpret our findings as suggesting that the valence-specific laterality hypothesis is supported only in certain circumstances. We discuss modulating factors, and we consider whether the mechanisms underlying those factors may be attentional or experiential in nature.     

The relationship between reading ability and lateralized lexical decision

Although lexical decision remains one of the most extensively studied cognitive tasks, very little is known about its relationship to broader linguistic performance such as reading ability. In a correlational study, several aspects of lateralized lexical decision performance were related to vocabulary and reading comprehension measures, as assessed using the Nelson-Denny Reading Test. This lateralized lexical decision task has been previously shown to demonstrate (1) independent contributions from both hemispheres, as well as (2) interhemispheric interactions during word recognition. Lexical decision performance showed strong relationships with both reading measures. Specifically, vocabulary performance correlated significantly with left visual field (LVF) word accuracy and LVF non-word latency, both measures of right hemisphere performance. There were also significant, though somewhat weaker, correlations between reading comprehension and RVF non-word latency. Lexicality priming, a measure of interhemispheric communication during lexical decision, was also correlated with reading comprehension. These results suggest that hemispheric interaction during word recognition is common, and that lexical processing contribution from the right hemisphere, something commonly taken as minor and inconsequential, can lead to significant performance benefits and to individual differences in reading.     

A new approach to cerebral asymmetry: RT differences in simultaneous bimanual finger movement during verbal and nonverbal tasks

This study was aimed at testing a new approach for examination of functional laterality based on hemispheric specialization. The subjects had to perform verbal (words/nonwords) and nonverbal (similar/different patterns) discrimination. The separation of the two hemispheres during information processing was realized by requiring a simultaneous response of both index fingers. The obtained over-all reaction times (RT) were faster for verbal than for pattern tasks. Considering the RTs for solely the particular, faster response of one or the other index finger, the right index finger turned out to be faster on verbal tasks whereas the left one dominated on pattern tasks. According to the hypothesis that the faster hand indicates the more active (contralateral) hemisphere, it can be assumed that words are responded to more quickly when processed in the left hemisphere. On the other hand, patterns are responded to more quickly when the right hemisphere is active. These results suggest that each hemisphere may be capable of processing verbal and nonverbal material; the speed of information processing, however, is faster in the more adept one.