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Lynn C Robertson

Publications and source records attributed to Lynn C Robertson.

15 recordsLinked to original sources
PubMed2007

Too many trees to see the forest: performance, event-related potential, and functional magnetic resonance imaging manifestations of integrative congenital prosopagnosia.

Neuropsychological, event-related potential (ERP), and functional magnetic resonance imaging (fMRI) methods were combined to provide a comprehensive description of performance and neurobiological profiles for K.W., a case of congenital prosopagnosia. We demonstrate that K.W.'s visual perception is characterized by almost unprecedented inability to identify faces, a large bias toward local features, and an extreme deficit in global/configural processing that is not confined to faces. This pattern could be appropriately labeled congenital integrative prosopagnosia, and accounts for some, albeit not all, cases of face recognition impairments without identifiable brain lesions. Absence of face selectivity is evident in both biological markers of face processing, fMRI (the fusiform face area [FFA]), and ERPs (N170). Nevertheless, these two neural signatures probably manifest different perceptual mechanisms. Whereas the N170 is triggered by the occurrence of physiognomic stimuli in the visual field, the deficient face-selective fMRI activation in the caudal brain correlates with the severity of global processing deficits. This correlation suggests that the FFA might be associated with global/configural computation, a crucial part of face identification.

Adult↗
PubMed2006

Cross-modal interactions in time and space: auditory influence on visual attention in hemispatial neglect.

Recent studies indicate that auditory tone presentation and auditory alerting can temporarily ameliorate visuospatial attention deficits in patients with unilateral neglect [Frassinetti, F., Pavani, F., & Ladavas, E. Acoustical vision of neglected stimuli: Interaction among spatially converging audiovisual inputs in neglect patients. Journal of Cognitive Neuroscience, 14, 62-69, 2002; Robertson, I. H., Mattingley, J. B., Rorden, C., & Driver, J. Phasic alerting of neglect patients overcomes their spatial deficit in visual awareness. Nature, 395, 169-172, 1998]. The current study investigated proposed mechanisms of cross-modal interaction to determine conditions in which auditory stimulation affects spatial and nonspatially lateralized attention deficits in a patient with hemispatial neglect. In Experiment 1, a target was presented among related distracters (conjunction search) while a tone was presented either bilaterally or in a congruent or incongruent spatial location with respect to the visual target. Whereas the results suggest a benefit of both general alerting and cross-modal spatial integration on visual search efficiency, the most significant improvement occurred when the target and tone were both presented in contralesional space. In Experiment 2, the effect of auditory alerting on selective attention was examined in a rapid serial visual search procedure with visual targets embedded in a stream of distracters presented at central fixation. When two targets were presented without an alerting tone, the patient missed the second target for up to 1000 msec after the first target appeared (a finding known as the "attentional blink" [AB] and, on average, about 400-500 msec in normals). An alerting tone presented at a fixed temporal location significantly reduced the AB in a tone-duration-dependent manner. Experiment 3 examined the effect of cross-modal space on selective attention in an AB paradigm in which T2 occurred randomly to the left or right of T1 with a spatially congruent or incongruent tone. Discrimination of T2 in contralesional space significantly improved when the tone was presented in the same location, and was impaired when the tone was presented on the ipsilesional side. The findings are discussed as they relate to cross-modal interactions and their influence on spatial and nonspatially lateralized attention deficits in neglect.

Acoustic Stimulation↗
PubMed2006

Processing the trees and the forest during initial stages of face perception: electrophysiological evidence.

Although configural processing is considered a hallmark of normal face perception in humans, there is ample evidence that processing face components also contributes to face recognition and identification. Indeed, most contemporary models posit a dual-code view in which face identification relies on the analysis of individual face components as well as the spatial relations between them. We explored the interplay between processing face configurations and inner face components by recording the N170, an event-related potential component that manifests early detection of faces. In contrast to a robust N170 effect elicited by line-drawn schematic faces compared to line-drawn schematic objects, no N170 effect was found if a pair of small objects substituted for the eyes in schematic faces. However, if a pair of two miniaturized faces substituted for the eyes, the N170 effect was restored. Additional experiments ruled out an explanation on the basis of miniaturized faces attracting attention independent of their location in a face-like configuration and show that global and local face characteristics compete for processing resources when in conflict. The results are discussed as they relate to normal and abnormal face processing.

Adolescent↗
PubMed2006

Coming unbound: disrupting automatic integration of synesthetic color and graphemes by transcranial magnetic stimulation of the right parietal lobe.

In some individuals, a visually presented letter or number automatically evokes the perception of a specific color, an experience known as color-grapheme synesthesia. It has been suggested that parietal binding mechanisms play a role in the phenomenon. We used a noninvasive stimulation technique, transcranial magnetic stimulation (TMS), to determine whether the posterior parietal lobe is critical for the integration of color and shape in color-grapheme synesthesia, as it appears to be for normal color-shape binding. Using a color-naming task with colored letters that were either congruent or incongruent with the synesthetic photism, we demonstrate that inhibition of the right posterior parietal lobe with repetitive TMS transiently attenuates synesthetic binding. These findings suggest that synesthesia (the induction of color from shape) relies on similar mechanisms as found in normal perception (where the perception of color is induced by wavelength).

Adult↗
PubMed2005

Crossing the midline: reducing attentional deficits via interhemispheric interactions.

Patients with unilateral neglect and extinction show a profound lack of awareness of stimuli presented contralateral to their lesion. However, many processes of perception are intact and contralesional stimuli seem to reach a high level of representation, perceptual and semantic. Some of these processes can work to decrease the magnitude of the attentional deficit. Here, we examine two of these intact processes, feature detection and perceptual grouping. First, we demonstrate that feature detection occurs in parallel in the contralesional visual fields of neglect and extinction patients. Second, we attempt to dissociate the influence of perceptual contours across the vertical meridian from the presence of an object or higher-level perceptual unit (or group) that may be created by these contours. We find that connections across the midline affect attentional deficits independently of the objects they may create. This suggests that several effects of grouping on neglect and extinction may be mediated by long-range cortical interactions that arise from connections across the vertical meridian.

Aged↗
PubMed2005

When blue is larger than red: colors influence numerical cognition in synesthesia.

In synesthesia, certain stimuli ("inducers") may give rise to perceptual experience in additional modalities not normally associated with them ("concurrent"). For example, color-grapheme synesthetes automatically perceive achromatic numbers as colored (e.g., 7 is turquoise). Although synesthetes know when a given color matches the one evoked by a certain number, colors do not automatically give rise to any sort of number experience. The behavioral consequences of synesthesia have been documented using Stroop-like paradigms, usually using color judgments. Owing to the unidirectional nature of the synesthetic experience, little has been done to obtain performance measures that could indicate whether bidirectional cross-activation occurs in synesthesia. Here it is shown that colors do implicitly evoke numerical magnitudes in color-grapheme synesthetes, but not in nonsynesthetic participants. It is proposed that bidirectional coactivation of brain areas is responsible for the links between color and magnitude processing in color-grapheme synesthesia and that unidirectional models of synesthesia might have to be revised.

Adult↗
PubMed2003

Posterior parietal cortex and the filtering of distractors.

Neural systems for visual processing can focus attention on behaviorally relevant objects, filtering out competing distractors. Neurophysiological studies in animals and brain imaging studies in humans suggest that such filtering depends on top-down inputs to extrastriate visual areas, originating in structures important for attentional control. To test whether the posterior parietal cortex may be a necessary source of signals that filter distractors, we measured the ability of a patient with bilateral parietal lesions to discriminate the features of a target surrounded by distractors of variable contrast. In the presence of distractors, the patient was impaired at discriminating both grating orientation and faces, and the magnitude of the impairment increased with distractor salience. These attentional deficits are remarkably similar to those caused by damage to monkey extrastriate regions V4 andor TEO, which are thought to be recipients of top-down attentional feedback. In contrast to the effects of V4 and TEO lesions, however, the parietal lesions impaired performance even with widely spaced targets and distractors, a finding consistent with the projections of parietal cortex to visual processing areas covering a wide range of receptive field sizes and eccentricities.

Aged↗
PubMed2003

Grouping influences in unilateral visual neglect.

Effects of grouping on unilateral neglect were investigated in 8 neurological patients with right hemisphere damage. It is well documented that arranging items to form a group spanning the midline decreases the magnitude of neglect. In the present study we examined how clusters of groups within the left or right visual field affect neglect and whether isolated groups within the neglected field deflect attention from right-sided displays. We orthogonally varied the strength of grouping on the right and left sides of a display and measured the time to find a predesignated target in one of those groups. Groups on the neglected left side did not affect right-sided target detection any more than an empty left page. However, strength of grouping did affect left sided target detection. These findings are discussed as they relate to attention and preattention in unilateral visual neglect.

Aged↗
PubMed2002

Attentional control and word inhibition in schizophrenia.

Previous studies have suggested that schizophrenia patients do not utilize contextual information efficiently to modulate attentional performance. The goal of the current study was to compare the utilization of context in modulating responses to irrelevant information on the Stroop task between a group of schizophrenia outpatients and matched controls. A single-trial version of the Stroop task was used to investigate performance on the Stroop task under three expectancy conditions. Eleven schizophrenia outpatients (on and off antipsychotic medication) and sixteen matched controls were tested. The schizophrenia patients showed: (1) augmented facilitation; (2) interference comparable to normals; and (3) normal ability to reduce interference under certain experimental circumstances. Schizophrenia patients were able to utilize contextual information under certain conditions and could modulate the magnitude of irrelevant word interference, although they were not able to overcome the prepotent tendency to read the word during the Stroop task as effectively as normals, which was reflected in greater Stroop facilitation. This suggests that the integrity or impairment of cognitive control functions in schizophrenia is related to the complexity of the context representation required to support that function.

Adult↗
PubMed2002

Visual field asymmetries and allocation of attention in visual scenes.

Single items such as objects, letters or words are often presented in the right or left visual field to examine hemispheric differences in cognitive processing. However, in everyday life, such items appear within a visual context or scene that affects how they are represented and selected for attention. Here we examine processing asymmetries for a visual target within a frame of other elements (scene). We are especially interested in whether the allocation of visual attention affects the asymmetries, and in whether attention-related asymmetries occur in scenes oriented out of alignment with the viewer. In Experiment 1, visual field asymmetries were affected by the validity of a spatial precue in an upright frame. In Experiment 2, the same pattern of asymmetries occurred within frames rotated 90 degrees on the screen. In Experiment 3, additional sources of the spatial asymmetries were explored. We conclude that several left/right processing asymmetries, including some associated with the deployment of spatial attention, can be organized within scenes, in the absence of differential direct access to the two hemispheres.

Adolescent↗
PubMed2002

Immediate versus sustained processing in schizophrenia.

A Stroop negative priming (NP) task was used to assess immediate selective attention and priming in schizophrenia and schizoaffective disorder. Subject groups were comprised of 12 state hospital inpatients (41.8 +/- 7.5 years of age), 11 outpatients (39.8 +/- 7.5 years of age), and 16 controls (36.4 +/- 11.7 years of age). Compared with the control group and the outpatients, inpatients failed to exhibit NP [F(2,36) = 6.09, p < .01], despite exhibiting equivalent Stroop RT interference (p > .05). Error rates did not differ significantly between the 3 groups. Although medication types and dosages were similar between the 2 patient groups, length of illness was significantly longer in the inpatients (19.8 years) than in the outpatients (12.4 years; p < .05). Positive symptom ratings were also significantly higher in the inpatients. The finding of reduced NP in the state hospital patients appears to be related to severity of symptomatology and chronicity of illness.

Adult↗
PubMed2002

Using reaction time to assess patients with unilateral neglect and extinction.

Brain damage often results in visual defects and/or higher order visuo-spatial disorders including the syndromes of unilateral neglect and extinction. These syndromes and their associated behavioral sequelae are described along with several standard assessments and methods for behaviorally quantifying such deficits. In particular, the advantages of the reaction time measures commonly used by cognitive neuroscientists are surveyed. In order to illustrate how reaction time measures can be used to examine the subtleties of visuo-spatial deficits, several reaction time studies that have been conducted in patients with neglect and/or extinction are discussed. These studies stand as an example of how reaction time measures can contribute to both clinical and experimental neuropsychology.

Attention↗
PubMed2002

Time course of inhibition and facilitation in patients with schizophrenia.

INTRODUCTION: Negative priming (NP) paradigms have been used extensively to understand the nature and time course of inhibitory deficits in patient populations. A majority of these studies have reported abnormal NP effects, with patients showing faster reaction times on NP sequences compared to the slowing displayed by controls. METHODS: A Stroop NP task was employed to measure immediate (within-trial) attentional processing as well as the sustainment (between-trial) of these processes in 12 medicated schizophrenia inpatients and 13 matched controls. Two response stimulus intervals (RSIs) were presented (500 ms and 2000 ms). Within-trial Stroop effects (interference and facilitation) and between-trial priming effects (negative and positive priming) were measured. Clinical symptomatology and duration of illness were also examined. RESULTS: At short RSIs of 500 ms, chronically ill state hospital schizophrenia patients failed to exhibit NP. In contrast, the control subjects exhibited normal NP at the short RSI but this priming faded at the long 2000 ms RSI and was no longer significant. The facilitatory priming effects remained stable across time in both groups. CONCLUSIONS: These results suggest that schizophrenia patients are better able to inhibit irrelevant stimuli that are immediate, but the sustainment of inhibition across very short time intervals (500 ms) may fade compared to controls.

Journal Article↗
PubMedDate not supplied

Reaching out to see: arm position can attenuate human visual loss.

Electrophysiological recordings in monkeys have now revealed several brain regions that contain bimodal visuotactile neurons capable of responding to either tactile or visual stimuli placed on or near the hands, arms, and face. These cells have now been found in frontal, parietal, and subcortical areas of the monkey brain, suggesting a cortical network of neurons that preferentially represent near peripersonal space. The degree to which the visual responses of such cells rely on input from the primary visual cortex and the extent to which they may contribute to visual perception is not completely understood. Nonetheless, recent neuropsychological studies suggest that a similar representation of near space may be bimodally coded in humans as well. Given the accumulating evidence for specialized processing of visual stimuli placed near the hands and arms, we hypothesized that arm position may be capable of modulating human visual ability. Here we report the case of WM, who lost his ability to see in his left visual hemifield after sustaining damage to his right primary visual cortex. Interestingly, the placement of WM's left arm into his "blind" field resulted in significantly better detection of left visual field stimuli compared to when his hand was placed in his lap at midline. Moreover, we found this attenuation to be confined to stimuli presented within reaching distance (unless a tool that extended WM's reach was held while he performed the test). These findings are highly consistent with the characteristics of the bimodal visuo-tactile neurons that have been described in monkeys. Thus, it seems that arm position can modulate human visual ability, even after damage to the primary visual cortex. This study provides an exciting bridge between monkey neurophysiology and human visual capacity while also offering a novel approach for improving visual defects acquired via cortical injury.

Aged↗