Céline Cavézian

Visual-Perceptual Abilities in Healthy Controls, Depressed Patients, and Schizophrenia Patients.

Previous studies have suggested a right hemineglect in schizophrenia, however few assessed possible visual-perceptual implication in this lateralized anomaly. A manual line bisection without (i.e., lines presented on their own) or with a local cueing paradigm (i.e., a number placed at one or both ends of the line) and the Motor-free Visual Perceptual Test-Vertical format (MVPT-V) were used to assess the visual-perceptual abilities of healthy controls, schizophrenia and depressed patients. Whereas healthy controls and depressed patients showed a non-significant leftward bias in manual line bisection, schizophrenia patients bisected significantly to the left of the true centre of the line. Interestingly, the pattern of performances in response to the local cueing paradigm was similar in depressed and schizophrenia patients such that both groups demonstrated a significant change in their bisection performance only in response to a cue placed at the right extremity of the line (control performance was modified by cues at either end of the line). Finally, in the MVPT-V, schizophrenia patients were impaired relative to the other two groups, especially in the spatial working memory and visual closure categories. These results suggest that: 1/a deficit towards the right hemifield, consistent with a mild form of right hemineglect, can be observed in schizophrenia; 2/lateralized anomalies could also be observed in depression using an appropriate tool such as manual line bisection; 3/performances in the MVPT-V suggested that a simple visual-perceptual deficit could not explain the lateralized anomaly observed in the manual line bisection, as it is the case in the hemineglect syndrome.

Pseudoneglect in schizophrenia: A line bisection study with cueing

Introduction. Numerous authors have reported the existence of lateralised abnormalities towards the right side in patients with schizophrenia. Methods. In the present study, a manual line bisection task was used to assess the existence of a visuospatial bias in patients with schizophrenia as compared to healthy subjects and left unilateral neglect patients. In addition, we used a local cueing paradigm (consisting of a number placed on the right, on the left, or at both ends of the line). Results. Healthy subjects showed a leftwards trend in the “no cue” condition (known as pseudoneglect) and neglect patients showed a right bias in all cue conditions. In contrast, patients with schizophrenia placed their manual estimation of the centre further to the left than healthy subjects in all cue conditions, reflecting neglect of the right side of the line. Moreover, like healthy subjects and neglect patients, patients with schizophrenia were affected by the local cueing. Conclusion. Hence, patients with schizophrenia show a bias in their spatial representation, which does not interfere with local context processing.

An fMRI Investigation of the Cortical Network Underlying Detection and Categorization Abilities in Hemianopic Patients

The current study aims to investigate visual scene perception and its neuro-anatomical correlates for stimuli presented in the central visual field of patients with homonymous hemianopia, and thereby to assess the effect of a right or a left occipital lesion on brain reorganization. Fourteen healthy participants, three left brain damaged (LBD) patients with right homonymous hemianopia and five right brain damaged (RBD) patients with left homonymous hemianopia performed a visual detection task (i.e. “Is there an image on the screen?”) and a categorization task (i.e. “Is it an image of a highway or a city?”) during a block-designed functional magnetic resonance imaging recording session. Cerebral activity analyses of the posterior areas—the occipital lobe in particular—highlighted bi-hemispheric activation during the detection task but more lateralized, left occipital lobe activation during the categorization task in healthy participants. Conversely, in patients, the same network of activity was observed in both tasks. However, LBD patients showed a predominant activation in their right hemisphere (occipital lobe and posterior temporal areas) whereas RBD patients showed a more bilateral activation (in the occipital lobes). Overall, our preliminary findings suggest a specific pattern of cerebral activation depending on the task instruction in healthy participants and cerebral reorganization of the posterior areas following brain injury in hemianopic patients which could depend upon the side of the occipital lesion.

Bisections in two languages: When number processing, spatial representation, and habitual reading direction interact

Calabria and Rossetti (2005) demonstrated that spatial biases related to the mental number line can be seen even when bisecting strings of number words. Strings of smaller magnitude number words were bisected further to the left than strings of larger magnitude number words. The current study investigated whether the left-to-right mental number line associated with number processing will result in similar spatial biases despite a habitual, right-to-left reading direction. Monolingual left-to-right readers were compared to bidirectional readers of English and Hebrew. Strings of Arabic numerals and of number words (e.g., THREE, EIGHT) were presented in separate conditions of English and Hebrew. Significant rightward biases were seen among native Hebrew readers, regardless of English reading level; whereas native English readers (both bidirectional and monodirectional) did not show significant biases to either the left or the right. The spatial bias in bisecting either Arabic numeral strings or number words was related to the habitual reading direction of the participant. There was no difference in spatial bias or for frequency of spatial bias based on numerical magnitude for either condition. We discuss the influence of cultural factors, such as reading direction and proficiency, on the representation of spatial and numerical material.

Visual aesthetic preference: Effects of handedness, sex, and age-related reading/writing directional scanning experience

Most studies of visual aesthetic preference report that right-handers prefer pictorial arrangements possessing left-to-right directionality and/or containing the region of greatest weight or interest on the right side. However, visual aesthetic preference has also been linked to directional scanning depending on the individual’s reading/writing habits. The present study aims to assess the respective role of biological factors, related to the functional specialization of the two cerebral hemispheres, indexed by handedness, and cultural factors (age-related reading/writing habits) in visual aesthetic preference. For this purpose, we tested the effects of handedness, sex and age on visual aesthetic preference in 40 children and 40 adults. Results revealed effects of handedness, sex, and age as well as a relationship between directional scanning, reading/writing habits and handedness. The question of a dynamic model of cerebral specialization based on interplay between cerebral plasticity and cultural/environmental factors is raised.

Schizophrenia and the Neglect Syndrome: Parietal Contributions to Cognitive Dysfunction in Schizophrenia

Many of the positive symptoms of schizophrenia, including hallucinations and passivity phenomena, have been related to dysfunction within association cortices. In addition, many of the cognitive deficits observed in patients with schizophrenia can also be characterised as impairments of higher level cognitions known to depend on these same association cortices. While most attention has been directed towards dysfunction of the frontal and temporal cortices, there is mounting evidence for impaired functioning of the parietal cortices as well. That is, there is a substantial body of research demonstrating impaired spatial and motor behaviours in patients with schizophrenia - behaviours known to depend on the parietal cortex. In this selective review we contrast some of these impairments with a neurological syndrome that commonly arises from damage to the right parietal cortex, known as unilateral neglect. Although the spatial impairments characteristic of neglect are far more severe than those observed in patients with schizophrenia, there are some important parallels that make the comparison worthwhile. We intend to outline those parallels and highlight ways in which they may inform models of schizophrenia.

Colour, face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental imagery disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional–exploratory mechanisms that are employed in visual behaviour.

Visuospatial processing in schizophrenia: Does it share common mechanisms with pseudoneglect?

Schizophrenia patients demonstrate behavioural and cerebral lateralised anomalies, prompting some authors to suggest they exhibit a mild form of right unilateral neglect. To better describe and understand lateralised visuospatial anomalies in schizophrenia, three experiments were run using tasks often utilised to study visuospatial processing in healthy individuals and in neglect patients: the Behavioural Inattention Test (BIT), the manual line bisection task with and without a local cueing paradigm, the landmark task (or line bisection judgement), and the number bisection task. Although the schizophrenia patients did not exhibit the full-blown neglect syndrome, they did demonstrate marked spatial biases that differentiated them from controls on all but two tasks. More specifically, schizophrenia patients showed neither a simple perceptual deficit nor an asymmetry, but demonstrated (1) lateralised anomalies on a simple manual line bisection task; (2) unilateral attentional deficits for line bisection within a local cueing paradigm; and (3) a lateralised deficit in the visuospatial representations of numbers. Altogether, these results suggest a right hemineglect-like deficit in schizophrenia in attentional, representational, and motor-intentional processes. Yet it does not appear to be as strong a phenomenon. Indeed, it could be considered as an accentuation of the normal asymmetry in visuospatial processing.

The letter height superiority illusion.

Letters are identified better when they are embedded within words rather than within pseudowords, a phenomenon known as the word superiority effect (Reicher in Journal of Experimental Psychology, 81, 275–280, 1969). This effect is, inter alia, accounted for by the interactive-activation model (McClelland & Rumelhart in Psychological Review, 88, 375–407, 1981) through feedback from word to letter nodes. In this study, we investigated whether overactivation of features could lead to perceptual bias, wherein letters would be perceived as being taller than pseudoletters, or words would be perceived as being taller than pseudowords. In two experiments, we investigated the effects of letter and lexical status on the perception of size. Participants who had to compare the heights of letters and pseudoletters, or of words and pseudowords, indeed perceived the former stimuli as being taller than the latter. Possible alternative interpretations of this height superiority effect for letters and words are discussed.

Neuropsychological deficits associated to cortical visual impairments

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