Order of feature recognition in familiar and unfamiliar faces

Three experiments measured order of processing for single faces presented to the left or right visual field (VF) using a same-different matching task. In contrast to earlier studies, the stimuli in the present experiments were carefully matched for overall similarity prior to the actual experiments. Experiments 1 and 2 showed that a significant top-to-bottom order of processing occurred for line drawings of unfamiliar faces but not for line drawings of familiar faces. Experiment 3 found evidence supporting top-to-bottom processing for unfamiliar photographic face stimuli. The photographic stimuli in Experiment 3 were matched more quickly when presented in the left VF (right hemisphere); however, this VF asymmetry was not related to previously reported differences in order of processing. It is suggested that under some conditions faces presented to the right hemisphere may be processed more like familiar faces than faces presented to the left hemisphere; however, this difference is not critical for the left VF (right hemisphere) superiority often found in face recognition tasks.     

Bilateral capacity for speech sound processing in auditory comprehension: evidence from Wada procedures

Data from lesion studies suggest that the ability to perceive speech sounds, as measured by auditory comprehension tasks, is supported by temporal lobe systems in both the left and right hemisphere. For example, patients with left temporal lobe damage and auditory comprehension deficits (i.e., Wernicke's aphasics), nonetheless comprehend isolated words better than one would expect if their speech perception system had been largely destroyed (70-80% accuracy). Further, when comprehension fails in such patients their errors are more often semantically-based, than-phonemically based. The question addressed by the present study is whether this ability of the right hemisphere to process speech sounds is a result of plastic reorganization following chronic left hemisphere damage, or whether the ability exists in undamaged language systems. We sought to test these possibilities by studying auditory comprehension in acute left versus right hemisphere deactivation during Wada procedures. A series of 20 patients undergoing clinically indicated Wada procedures were asked to listen to an auditorily presented stimulus word, and then point to its matching picture on a card that contained the target picture, a semantic foil, a phonemic foil, and an unrelated foil. This task was performed under three conditions, baseline, during left carotid injection of sodium amytal, and during right carotid injection of sodium amytal. Overall, left hemisphere injection led to a significantly higher error rate than right hemisphere injection. However, consistent with lesion work, the majority (75%) of these errors were semantic in nature. These findings suggest that auditory comprehension deficits are predominantly semantic in nature, even following acute left hemisphere disruption. This, in turn, supports the hypothesis that the right hemisphere is capable of speech sound processing in the intact brain.     

Language, perception, and the schematic representation of spatial relations

Schemas are abstract nonverbal representations that parsimoniously depict spatial relations. Despite their ubiquitous use in maps and diagrams, little is known about their neural instantiation. We sought to determine the extent to which schematic representations are neurally distinguished from language on the one hand, and from rich perceptual representations on the other. In patients with either left hemisphere damage or right hemisphere damage, a battery of matching tasks depicting categorical spatial relations was used to probe for the comprehension of basic spatial concepts across distinct representational formats (words, pictures, and schemas). Left hemisphere patients underperformed right hemisphere patients across all tasks. However, focused residual analyses using voxel-based lesion-symptom mapping (VLSM) suggest that (1) left hemisphere deficits in the representation of categorical spatial relations are difficult to distinguish from deficits in naming these relations and (2) the right hemisphere plays a special role in extracting schematic representations from richly textured pictures.     

Interhemispheric categorization of pictures and words

Earlier studies suggest that interhemispheric processing increases the processing power of the brain in cognitively complex tasks as it allows the brain to divide the processing load between the hemispheres. We report two experiments suggesting that this finding does not generalize to word-picture pairs: they are processed at least as efficiently when processed by a single hemisphere as compared to processing occurring between the two hemispheres. We examined whether dividing the stimuli between the visual fields/hemispheres would be more advantageous than unilateral stimulus displays in the semantic categorization of simultaneously presented pictures, words, and word-picture pairs. The results revealed that within-domain stimuli (semantically related picture pairs or word pairs) were categorized faster in bilateral than in unilateral displays, whereas cross-domain stimuli (word-picture pairs) were not categorized faster in bilateral than in unilateral displays. It is suggested that interhemispheric sharing of word-picture stimuli is not advantageous as compared to unilateral processing conditions because words and pictures use different access routes, and therefore, it may be possible to process in parallel simultaneously displayed word-picture stimuli within a single hemisphere.     

In Your Right Mind: Right Hemisphere Contributions to Language Processing and Production

The verbal/nonverbal account of left and right hemisphere functionality is the prevailing dichotomy describing the cerebral lateralization of function. Yet the fact that the left hemisphere is the superior language processor does not necessarily imply that the right hemisphere is completely lacking linguistic ability. This paper reviews the growing body of research demonstrating that, far from being nonverbal, the right hemisphere has significant language processing strength. From prosodic and paralinguistic aspects of speech production, reception, and interpretation, to prelexical, lexical and postlexical components of visual word recognition; strong involvement of the right hemisphere is implicated. The evidence reviewed challenges the notion that language is solely a function of the “verbal” left hemisphere, indicating that the right cerebral hemisphere makes significant and meaningful contributions to normal language processing as well.     

Hemispheric processing deficits in patients with paranoid schizophrenia

The purpose of the present study was to investigate hemispheric deficits in individuals with paranoid schizophrenia on four kinds of tasks: dichoptic viewing tasks involving verbal and nonverbal visual stimuli, and dichotic listening tasks involving verbal and nonverbal auditory stimuli. As dependent measures, both accuracy and speed of (correct) responding were measured. The sample recruited for this study consisted of 18 patients with paranoid schizophrenia, 15 outpatients with anxiety disorders, and 20 controls with no history of psychiatric disorders. Results indicated that, relative to the controls, the paranoid schizophrenic patients were less accurate and less efficient on auditory-verbal tasks requiring right hemisphere processing. Unlike the controls the paranoid schizophrenic patients manifested a lateralized left hemisphere advantage.     

Hemispheric Processing Deficits in Patients with Paranoid Schizophrenia

The purpose of the present study was to investigate hemispheric deficits in individuals with paranoid schizophrenia on four kinds of tasks: dichoptic viewing tasks involving verbal and nonverbal visual stimuli, and dichotic listening tasks involving verbal and nonverbal auditory stimuli. As dependent measures, both accuracy and speed of (correct) responding were measured. The sample recruited for this study consisted of 18 patients with paranoid schizophrenia, 15 outpatients with anxiety disorders, and 20 controls with no history of psychiatric disorders. Results indicated that, relative to the controls, the paranoid schizophrenic patients were less accurate and less efficient on auditory-verbal tasks requiring right hemisphere processing. Unlike the controls, the paranoid schizophrenic patients manifested a lateralized left hemisphere advantage.     

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.     

Left hemispheric interference with nonverbal performance in aphasics: comparison with data from split-brain studies

Two nonverbal tasks (Nebes' Figural Unification Test and Arc-Circle Matching Task) were given to 10 aphasic patients and 10 normal controls. Observations in split-brain patients have shown that the right hemisphere performs almost normally on these tasks while the left hemisphere fails completely. Left and right hand performances of aphasics and controls were compared with those of split-brain patients as reported in the literature. In the Figural Unification Test the aphasics' left hand performance was significantly poorer than that of split-brain patients. This is interpreted as an effect of left hemispheric interference with right hemispheric nonverbal performance. The lack of a similar impairment of left hand performance in the Arc-Circle Matching Task suggests that this interference is only provoked by tasks which, due to the possible verbalization of stimulus material, tend to stimulate left hemispheric activity.     

Asymmetrical hemisphere activation enhances global–local processing

Decades of research focusing on the neurophysiological underpinnings related to global–local processing of hierarchical stimuli have associated global processing with the right hemisphere and local processing with the left hemisphere. The current experiment sought to expand this research by testing the causal contributions of hemisphere activation to global–local processing. To manipulate hemisphere activation, participants engaged in contralateral hand contractions. Then, EEG activity and attentional scope were measured. Right-hand contractions caused greater relative left-cortical activity than left-hand contractions. Participants were more narrowly focused after left-hemisphere activation than after right-hemisphere activation. Moreover, N1 amplitudes to local targets in the left hemisphere were larger after left-hemisphere activation than after right-hemisphere activation. Consistent with past research investigating hemispheric asymmetry and attentional scope, the current results suggest that manipulating left (right) hemisphere activity enhanced local (global) attentional processing.     

Hemispheric differences in semantic processing: Category matching is not the same as category membership

Two closely related semantic processing tasks were studied under identical procedural conditions in order to examine lateral visual field effects on reaction times. In Experiment 1, reaction times did not differ as a function of visual field when subjects decided whether a lateral word was a member of a foveally presented category word (category membership task). On the other hand, reaction times were faster for right than for left visual field stimulus presentations when subjects decided whether two words, one lateral and one foveal, belonged to the same category (category matching task), although this advantage did not occur immediately. In Experiment 2, the laterality effect in the category matching task was studied as a function of word familiarity. Two groups of subjects performed the matching task for two blocks of trials, one group receiving the same word list in each block and the other receiving different lists. No visual field differences in reaction times were observed for either group during the first block of trials, but a distinct right field advantage appeared for both during the second block. The data from these experiments suggest that category matching strategies rely upon structures or processes localized in the left hemisphere, although their influence is not immediate. Category membership strategies, on the other hand, do not depend upon such localized structures.     

Searching for patterns in random sequences.

In a probability-guessing paradigm, participants predict which of two events will occur on each trial. Participants generally frequency match even though frequency matching is nonoptimal with random sequences. The optimal strategy is to guess the most frequent event, maximizing. We hypothesize that frequency matching results from a search for patterns, even in random sequences. Using both callisotomy patients and patients with frontal brain damage, Wolford, Miller, and Gazzaniaga (2000) found frequency matching in the left hemisphere but maximizing in the right hemisphere. In this paper, we show that a secondary task that competes for left hemisphere resources moves the participants toward maximizing but that a right-hemisphere task preserves frequency matching. We also show that a misunderstanding of randomness contributes to frequency matching.     

Perceptual biases in processing facial identity and emotion

Normal observers demonstrate a bias to process the left sides of faces during perceptual judgments about identity or emotion. This effect suggests a right cerebral hemisphere processing bias. To test the role of the right hemisphere and the involvement of configural processing underlying this effect, young and older control observers and patients with right hemisphere damage completed two chimeric faces tasks (emotion judgment and face identity matching) with both upright and inverted faces. For control observers, the emotion judgment task elicited a strong left-sided perceptual bias that was reduced in young controls and eliminated in older controls by face inversion. Right hemisphere damage reversed the bias, suggesting the right hemisphere was dominant for this task, but that the left hemisphere could be flexibly recruited when right hemisphere mechanisms are not available or dominant. In contrast, face identity judgments were associated most clearly with a vertical bias favouring the uppermost stimuli that was eliminated by face inversion and right hemisphere lesions. The results suggest these tasks involve different neurocognitive mechanisms. The role of the right hemisphere and ventral cortical stream involvement with configural processes in face processing is discussed.     

A noninvasive index of hemispheric activity

Tympanic thermometers were used to measure fluctuations in the temperature of the left and right hemispheres of 22 normal high school students while performing verbal and nonverbal visual discrimination tasks. The nonverbal task involving face recognition demonstrated the predicted effect of hemispheric bias on performance: The subjects performed better when they showed a relative rise in right-hemisphere temperature. No significant relationship between hemispheric temperature and level of performance was observed during the verbal task, perhaps owing to the opportunity to treat effectively the nonwords as either linguistic strings or visual patterns. It is concluded that tympanic temperature effectively measures hemispheric activity during cognitive processing.     

Interhemispheric interaction in word‐ and color‐matching of Kanji color words1

Abstract: The aim of the present study was to investigate the possibility that a shift toward a within‐hemisphere advantage would emerge when two stimulus items receive, respectively, different processing (vs. when they receive similar processing). Using right‐handed participants, we briefly presented two Kanji color‐word items as either within‐field or across‐fields. Viewers had to match the two items in terms of ink color (a color‐matching task) or word meaning (a name‐matching task). Each Kanji color word was presented with the same (congruent) or different (incongruent) ink color relative to the word meaning. Our results were twofold. First, a within‐field advantage appeared in the relatively easier color‐matching task, whereas an across‐field advantage tended to occur in the relatively harder name‐matching task. Second, in the word‐matching task an across‐field advantage appeared when both Kanji color words appeared in similar processing manners (both congruent or both incongruent), whereas a within‐field advantage occurred when processing of two Kanji items differed (one congruent and one incongruent). These results suggested that a shift toward a within‐hemisphere advantage occurs when two items are processed in respectively different ways.     

Binary-choice decision time depends upon cerebral hemisphere and nature of task

Binary-choice paradigms are classificatory problems of basic importance to the understanding of elementary decision processes. Generally when subjects decide if two visual stimuli are identical or differ by as little as one element, the decision of "Different" takes longer. This finding is unexpected as decisions of "Different" should not require an exhaustive matching of elements. Using stimulus presentation to the right and left cerebral hemispheres, the right hemisphere initiated fast selections of "Same" for figural material and alone was responsible for the "Same"/"Different" response differential. Exp. 1 (n = 22) gave no differences for same-different, unilateral-bilateral stimulation, and left-right hemispheres. Exp. 2, using word meaning as the binary-choice task, also showed faster decisions for "Same" but a different left-hemisphere-dependent strategy. The nature of information processing in relation to binary-choice tasks is discussed and the utility of bihemispheric paradigms is demonstrated.     

Form-specific visual priming for new associations in the right cerebral hemisphere

In three experiments, we examined the internal processing mechanisms of relatively independent visual-form subsystems. Participants first viewed centrally presented word pairs and then completed word stems presented beneath context words in the left or right visual field. Letter-case-specific priming in stem completion was found only when the context word was the same word that had previously appeared above the primed completion word and the items were presented directly to the right cerebral hemisphere. This pattern of results was not found when participants deliberately recollected previously presented words when completing the stems. Results suggest that holistic processing, not parts-based processing as assumed in many contemporary theories of visual-form recognition, is performed in a subsystem that distinguishes specific instances in the same abstract category of form and that operates more effectively in the right hemisphere than in the left hemisphere.     

Impairments of nonverbal oral movements after left hemisphere damage: A followup analysis of errors

Acquisition of a task requiring the imitation of a series of nonverbal oral movements is most severely impaired in patients with aphasic disturbance. However, nonaphasic patients with left hemisphere damage also perform more poorly than patients with right hemisphere damage or normal control subjects. Analysis of the errors made on the multiple oral movements task reveals that left, but not right, hemisphere damage is highly associated with perseverative responses. Patients with right hemisphere damage do not differ significantly from normal control subjects in the acquisition of or in the type of errors made on the task. It is suggested that the left hemisphere plays an important role in the control of nonverbal oral movement production.     

Hemispheric specialization in reading and word recognition

Three experiments dealing with hemispheric specialization are presented. In Experiment 1, words and/or faces were presented tachistoscopically to the left or right of fixation. Words were more accurately identified in the right visual field and faces were more accurately identified in the left visual field. A forced choice error analysis for words indicated that errors made for word stimuli were most frequently visually similar words and this effect was particularly pronounced in the left visual field. Two additional experiments supported this finding. On the basis of the results, it was argued that word identification is a multistage process, with visual feature analysis carried out by the right hemisphere and identification and naming by the left hemisphere. In addition, Kinsbourne's attentional model of brain function was rejected in favor of an anatomical model which suggests that simultaneous processing of verbal and nonverbal information does not constrict the attention of either hemisphere.     

Cerebral mechanisms for understanding emotional prosody in speech

Hemispheric contributions to the processing of emotional speech prosody were investigated by comparing adults with a focal lesion involving the right (n = 9) or left (n = 11) hemisphere and adults without brain damage (n = 12). Participants listened to semantically anomalous utterances in three conditions (discrimination, identification, and rating) which assessed their recognition of five prosodic emotions under the influence of different task- and response-selection demands. Findings revealed that right- and left-hemispheric lesions were associated with impaired comprehension of prosody, although possibly for distinct reasons: right-hemisphere compromise produced a more pervasive insensitivity to emotive features of prosodic stimuli, whereas left-hemisphere damage yielded greater difficulties interpreting prosodic representations as a code embedded with language content.