Egocentric frame of reference: its role in spatial bias after right hemisphere lesions.

The reference shift hypothesis of unilateral neglect holds that spatial bias in left neglect stems from a rightward deviation of patients' egocentric frame of reference (ER). Twenty five unselected right brain-damaged patients participated in a straight-ahead pointing task to assess the position of their ER (Experiment 1). A rightward ER shift emerged only in the subgroup of patients with extensive parietal lesions. In Experiment 2, we found that the position of the ER did not predict the outcome of various visuospatial neglect tests (r = 0.07 to 0.27). In Experiment 3, no significant positive correlation emerged between the ER position and visual (r = 0.26) or tactile (r = -0.48) extinction. Two further experiments examined the relationships between the ER position and patients' performance on a reaction time test of directional motor bias (Experiment 4), and on a test of response times to lateralised visual stimuli (Experiment 5). Results showed that the ER position did not predict the distribution of accuracy scores or response times in either task (Experiment 3: accuracy: r = 0.06; response times: r = 0.16; Experiment 4: accuracy: r = 0.09; response times: r = 0.04). We concluded that the position of the ER plays no crucial role in the behavioural consequences of spatial bias induced by right hemisphere lesions.     

Contextual bias and predictive inferencing in adults with and without right hemisphere brain damage

Background: Impaired inferencing has been suggested to contribute to the comprehension deficits exhibited by adults with right hemisphere brain damage (RHD); however, conflicting results exist concerning the inferencing deficits associated with RHD. Although inference generation has been examined in most of the previous studies, little information is available regarding other processes, such as maintaining inferences over time, the plausibility of inferences in different contexts, and how contextual bias affects these inferencing processes.Aims: The purpose of the study was to examine the influence of contextual bias on the inferencing processes of older adults without brain damage (NBD) and adults with RHD. It was expected that the NBD group would show clear effects of contextual bias. In contrast, the RHD group was expected to use strong contextual bias to guide inferencing, but to have more difficulty in stories that contained weaker contextual bias.Methods & Procedures: A total of 18 older adults without brain damage and 8 individuals with RHD participated in the study. Participants in the RHD group were selected on the basis of a lesion in the right hemisphere, and not the presence of a communication disorder. None evidenced neglect, and as a group they performed similarly to the NBD group on measures of language and working memory. Thinking Out Loud protocols were used to examine the generation, maintenance, and likelihood of predictive inferences, as well as generation of alternative inferences in stories with a low or high probability that a specific outcome would occur. The study was constructed as a mixed design, with group as a between-subjects variable and story condition as a within-subjects variable.Outcomes & Results: Results suggest that contextual bias influenced inference processes in both healthy older adults and individuals with RHD. Both groups used context to qualify the likelihood of inferences, but adults with RHD were less adept at using context to maintain inferences and to restrict inference generation to the most likely outcomes.Conclusions: Adults with RHD who have minimal language deficits can generate predictive inferences and use context to guide some inferencing processes, although they do not use context to constrain inferencing as much as healthy older adults do. The results provide potential insight into the nature of comprehension deficits that may occur after RHD, but the small sample of individuals with minimal cognitive-communication impairments precludes generalisation of the findings to the larger clinical population of adults with RHD.     

A right hemisphere bias towards false memory

Previous studies suggest that leftward cradling bias may facilitate mother–infant relationships, as it preferentially locates the infant in the mother's left hemi-space, which is specialized for several social-affective processes. If leftward cradling bias is mediated by social-affective attachment processes, it should be reduced in humans who are deficient in such processes. Individuals diagnosed with Autism Spectrum Disorders (ASDs) constitute a population with known deficits in social and emotional relating. A pilot study confirmed reduced bias in this group, and in the present study, we elaborated methods to assess also the impact of higher cognitive processes on cradling bias. Direct systematic observation was used to investigate the occurrence of cradling bias in ASD, non-ASD intellectually disabled children and typically developing children. Ninety-three participants aged 5–15 years cradled a life-like doll on four separate occasions. Intelligence and executive functions were assessed. Regression analyses revealed that ASD diagnosis was the only significant predictor of atypical cradling preference. While intellectually disabled and typically developing children clearly preferred to cradle to the left, no preference was evident in the ASD group. Results support the hypothesis that leftward cradling bias is associated with basic social-affective capacities.     

A right hemisphere bias towards false memory

We extend to English Ito's (2001) demonstration of a hemispheric asymmetry in a false recognition and list-learning paradigm in Japanese. We show for English a significant interaction between the hemifield to which the probe word was presented and the probe type (non-studied but semantically related to the studied words versus non-studied and semantically unrelated to the studied words). The right hemisphere performed less well in rejecting the semantically related "lures"; the left hemisphere performed better in rejecting the semantically novel unstudied words. We discuss the results in terms of a model of fine semantic coding in the LH and coarse semantic coding in the RH, together with the dependence on memory probes that retain the representational signature of the hemisphere to which they were initially projected. Sex of the participants was also included as an independent variable; the results suggested that most of the effect lay with the female participants.     

Graviceptive misperception of the postural vertical after right hemisphere damage

We have systematically studied the subjective postural vertical (SPV) and the location of the centre of gravity (COG) in right brain damaged patients, classified according to the severity of their hemispatial neglect. The results indicate that the patients lean towards the side of space where they feel aligned with their ipsilesionally displaced SPV, resulting in a ipsilesional deviation of the COG. This displacement can be reduced by the effect of contralesionally applied transcutaneous electrical nerve stimulation (TENS). However, in the severe neglect patients, an increasing mismatch arose between the perceived body orientation and the direction of the gravitational force. The results indicate that this conflict is compensated by a contraversive shift of the COG towards the contraversive side in order to re-align the SPV with the gravitational vertical.     

Alignment following left and right hemisphere damage

Background: Patients with fluent aphasia have been reported to exhibit abnormal timing of some linguistic units, but the basis of this deficit is unclear. It has been hypothesised that these patients have impaired ability to control temporal information stored in lexical items, but timing at the level of intonation phrase (IP) is intact for them. One aspect of temporal control at the level of IP is alignment, the relative timing of events in fundamental frequency (F0) contours associated with intonation and events in the segmental string.

Aim: The present study sought to determine whether patients with fluent aphasia have intact ability for alignment.

Methods & Procedures: Absolute and relative measures of intervals between F0 peaks and valleys, as well as syllable duration were evaluated in sentences produced by patients with fluent aphasia, nonfluent aphasia, right hemisphere damage (RHD), and a group of neurologically normal individuals. The productions were evaluated perceptually by five neurologically normal native speakers.

Outcomes & Results: The patients with fluent aphasia performed poorly on absolute and relative measures of alignment. Their nonfluent counterparts exhibited abnormally long absolute durations on all measures including final syllable length, and the RHD performed comparably with the control participants on both absolute and relative measures of alignment and syllable duration. All groups were perceptually indistinguishable.

Conclusion: The data for all three groups of patients are consistent with previous reports on speech timing following brain damage. The performance of the patients with fluent aphasia on alignment does not support the view that these patients have intact ability for speech timing at the level of IP.     

Residual rightward attentional bias after apparent recovery from right hemisphere damage: implications for a multicomponent model of neglect.

Unilateral neglect may be a multicomponent attentional disorder consisting of an initial automatic orienting of attention toward the ipsilesional side and a subsequent impairment in contralesionally reorienting attention, both of which are superimposed on a generalised reduction in attention resources. It has been hypothesised that patients' ability to reorient attention contralesionally may recover relatively quickly, but that the ipsilesional attention bias may be relatively persistent. This hypothesis was tested by consecutively examining 13 patients who had had a right hemisphere stroke, and who had left unilateral neglect. They were examined once shortly after the stroke and again 12 months later, using a battery of standard clinical and experimental tasks. Patients initially showed a strong and consistent rightward attentional bias in addition to a failure to reorient their attention leftward. After 12 months patients continued to show an abnormal ipsilesional attentional bias, though most were now able to fully reorient their attention toward the contralesional side. These results suggest that restitution of the capacity to reorient attention contralesionally may underlie the apparent recovery from clinical signs of unilateral neglect. The presence of a residual ipsilesional attentional bias in most patients, however, may, at least in part, account for the poor functional outcomes in some apparently "recovered" patients.     

Unilateral spatial neglect: a dramatic but often neglected consequence of right hemisphere damage

INTRODUCTION: Unilateral Spatial Neglect (USN) is a common consequence of right brain damage. In the most severe cases, behavioral signs of USN can last several years and compromise patients' autonomy and social rehabilitation. These clinical facts stress the need for reliable procedures of diagnosis and rehabilitation. STATE OF THE ART: The last 3 decades have witnessed an explosion of studies on USN, which raises issues related to complex cognitive activities such as mental representation, spatial attention and consciousness. USN is probably a heterogeneous syndrome, but some of its underlying mechanisms might be understood as an association of disorders of spatial attention. A bias of automatic orienting towards right-sided objects seems typical of left USN. Afterwards, patients find it difficult to disengage their attention in order to explore the rest of the visual scene. Neglected objects are sometimes processed in an "implicit" way. PERSPECTIVES: The development of behavioural paradigms and of neuroimaging techniques and their application to the study of USN has advanced our understanding of the functional mechanisms of attention and spatial awareness, as well as of their neural bases. A number of new procedures for rehabilitation have recently been proposed. CONCLUSION: The present review describes the clinical presentation of USN, its anatomical basis and some of possible accounts of different aspects of neglect behavior. Results of computer simulations and of rehabilitation techniques are also presented with implications for the functioning of normal neurocognitive systems.     

Impaired grating discrimination following right hemisphere damage

We investigated the effect of unilateral brain lesions on visual discrimination of low-, middle- and high-frequency gratings. The performance of patients with right hemisphere lesions was significantly impaired compared with that of both controls and patients with left hemisphere lesions. This impairment was largely limited to patients with right posterior hemispheric lesions and was present with all spatial frequencies. These findings run counter to the hypothesis that high and low spatial frequencies are preferentially processed by different hemispheres.     

Sensitivity of clinical and behavioural tests of spatial neglect after right hemisphere stroke

OBJECTIVES: The lack of agreement regarding assessment methods is responsible for the variability in the reported rate of occurrence of spatial neglect after stroke. The aim of this study was to assess the sensitivity of different tests of neglect after right hemisphere stroke. METHODS: Two hundred and six subacute right hemisphere stroke patients were given a test battery including a preliminary assessment of anosognosia and of visual extinction, a clinical assessment of gaze orientation and of personal neglect, and paper and pencil tests of spatial neglect in the peripersonal space. Patients were compared with a previously reported control group. A subgroup of patients (n=69) received a behavioural assessment of neglect in daily life situations. RESULTS: The most sensitive paper and pencil measure was the starting point in the cancellation task. The whole battery was more sensitive than any single test alone. About 85% of patients presented some degree of neglect on at least one measure. An important finding was that behavioural assessment of neglect in daily life was more sensitive than any other single measure of neglect. Behavioural neglect was considered as moderate to severe in 36% of cases. A factorial analysis revealed that paper and pencil tests were related to two underlying factors. Dissociations were found between extrapersonal neglect, personal neglect, anosognosia, and extinction. Anatomical analyses showed that neglect was more common and severe when the posterior association cortex was damaged. CONCLUSIONS: The automatic rightward orientation bias is the most sensitive clinical measure of neglect. Behavioural assessment is more sensitive than any single paper and pencil test. The results also support the assumption that neglect is a heterogeneous disorder.     

Idiosyncratic word associations following right hemisphere damage

Single oral word associations produced by right-hemisphere-damaged (RHD) stroke patients and age-matched healthy controls were analyzed to assess the right-hemisphere contribution to lexical-semantic processes. RHD patients did not differ from normals in terms of response times, in syntactic class of the response word, or in numbers of errors in response to words drawn from different grammatical categories and words differing in imageability/concreteness. Groups also did not differ in the number of high frequency, popular, associations produced. Despite their apparently intact ability to access high-frequency lexical associates, RHD patients, particularly those with frontal-lobe lesions, also sporadically produced lexical responses that were idiosyncratically related or that were totally unrelated to the stimulus word. An attentional disorder is suggested to explain these pragmatically deviant lexical associations.     

Eye-catching: right hemisphere attentional bias for emotional pictures

To examine whether healthy individuals spontaneously direct attention to emotional pictures, eye movements were monitored continuously during the presentation of pairs of emotional and neutral pictures. A right hemisphere advantage was expected for initial orienting to emotional pictures. When an emotionally arousing picture was presented in the left visual hemifield, i.e., to the right hemisphere, the initial saccade was more often issued towards it, irrespective of valence. Negative pictures did not lead to avoidance throughout the 8-second trials; rather, both positive and negative valence held attention. This study adds to the evidence that overt attention to visual stimuli is boosted by emotion and that there is a right hemisphere advantage for orienting to emotional cues.     

Laterally directed arm movements and right unilateral neglect after left hemisphere damage.

Signs of unilateral neglect for events occurring in one hemispace most often result from right hemisphere lesions. Right unilateral neglect after left hemisphere damage is much rarer, and has received less attention. The present study explores the relationships between right unilateral neglect and asymmetries in producing laterally directed arm movements in the horizontal plane in left brain-damaged (LBD) patients. Participants produced right- or left-directed arm movements with their left arm in response to centrally located visual stimuli. Results showed that LBD patients with signs of right unilateral neglect were consistently slowed when producing arm movements toward the right (neglected) side, as compared to left-directed movements. Taking into account patients with and without signs of neglect, this directional asymmetry positively correlated with a reaction-time measure of perceptual spatial bias. These findings stand in contrast with previous results obtained with the same experimental paradigm in right brain-damaged patients, in whom a consistent slowing of leftward-directed movements was rare and apparently unrelated to the presence and severity of left neglect. These conflicting results are discussed with respect to the hypothesis that different mechanisms may underlie left and right unilateral neglect.     

Disturbance of rhythm sense following right hemisphere damage

In a patient with right temporal lobe and additional right basal ganglia damage following a stroke, recognition and reproduction of simple rhythmical Gestalten were examined and found grossly undisturbed. In contrast to this undisturbed perception and production of rhythm, the patient could not tap or move rhythmically in beat with an auditory pacer such as a metronome or marching band music, yet he could do so to rhythmically presented light or touch stimuli. Thus, the impairment seems to be a previously undescribed, modality specific disturbance of auditorily paced predictive motor behavior affecting, for example, walking, dancing, singing and speech.     

A case of impaired auditory and visual speech prosody perception after right hemisphere damage

It is well established that vision plays a role in segmental speech perception, but the role of vision in prosodic speech perception is less clear. We report on the difficulties in prosodic speech perception encountered by KB after a right hemisphere stroke. In addition to musical deficits, KB was suspected of having impaired auditory prosody perception. As expected, KB was impaired on two prosody perception tasks in an auditory-only condition. We also examined whether the addition of visual prosody cues would facilitate his performance on these tasks. Unexpectedly, KB was also impaired on both tasks under visual-only and audio-visual conditions. Thus, there was no evidence that KB could integrate auditory and visual prosody information or that he could use visual cues to compensate for his deficit in the auditory domain. In contrast, KB was able to identify segmental speech information using visual cues and to use these visual cues to improve his performance when auditory segmental cues were impoverished. KB was also able to integrate audio-visual segmental information in the McGurk effect. Thus, KB's visual deficit was specific to prosodic speech perception and, to our knowledge, this is the first reported case of such a deficit.     

A bias for the female face in the right hemisphere

In the present study we assessed the contribution of the two hemispheres to the attribution of gender of faces in male and female observers. Normal and chimeric faces were presented in their canonical orientation and upside-down in a tachistoscopic paradigm. Chimeric faces were composed of two halves (left and right) obtained from photos of individuals of the same sex or from individuals of different sexes. All faces were presented tachistoscopically with a central fixation, the two halves falling in the two visual fields of the observer, who was required to rapidly judge the sex of the face. A left half-face (right-hemispheric) bias for gender attribution with upright faces was observed both in male and female participants, as previously reported. Strikingly, however, the bias depended entirely on female-left/male-right chimeras, revealing a right-hemispheric advantage for the recognition of female faces. The results are discussed in the light of a behavioural bias during development (i.e., maternal cradling).     

A bias for the female face in the right hemisphere

In the present study we assessed the contribution of the two hemispheres to the attribution of gender of faces in male and female observers. Normal and chimeric faces were presented in their canonical orientation and upside-down in a tachistoscopic paradigm. Chimeric faces were composed of two halves (left and right) obtained from photos of individuals of the same sex or from individuals of different sexes. All faces were presented tachistoscopically with a central fixation, the two halves falling in the two visual fields of the observer, who was required to rapidly judge the sex of the face. A left half-face (right-hemispheric) bias for gender attribution with upright faces was observed both in male and female participants, as previously reported. Strikingly, however, the bias depended entirely on female-left/male-right chimeras, revealing a right-hemispheric advantage for the recognition of female faces. The results are discussed in the light of a behavioural bias during development (i.e., maternal cradling).     

Motor deficits after left or right hemisphere damage due to stroke or tumor

The motor performance of 29 tumor and 43 stroke patients with unilateral left or right hemisphere damage and 40 non-brain-damaged control subjects was compared on six motor tasks. Grip strength, finger tapping, static and vertical groove steadiness, maze coordination and grooved pegboard tasks were administered. All brain-damaged groups performed more poorly than the control group on the hand contralateral to the lesion on all tasks and on the hand ipsilateral to the lesion on the tasks which required greater sensory-motor interaction (static and vertical groove steadiness, maze coordination and grooved pegboard). This pattern of results was the same for the patients with left or right hemisphere damage and was best explained by the hypothesis that the tasks which require greater sensory-motor interaction require more neural control and are more likely to be disrupted after brain damage, regardless of lateralization.