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PubMed2006

The flash-lag effect is reduced when the flash is perceived as a sensory consequence of our action.

The flash-lag effect (FLE) is defined as an error in localization that consists of perceiving a flashed object to lag behind a moving one when both are presented in physical alignment. Previous studies have addressed the question if it is the predictability of the flash, or the moving object, that modulates the amount of the error. However, the case when the flash is self-generated, and hence can be internally predicted, has not yet been addressed. In Experiment 1, we compare four conditions: flash unpredictable, flash externally predicted by a beep, flash internally generated (and predicted) by pressing a key, and flash triggered by a key press but temporally unpredictable. The FLE was significantly reduced only when the flash was internally predictable. In Experiment 2, we rule out the possibility that the reduction of the FLE was due to the use of the key press as a temporal marker. We conclude that when the flash is perceived as a sensory consequence of our own action, its detection can be speeded up, thereby resulting in a reduction of the FLE. A third experiment supports this interpretation. The mechanism by virtue of which the detection is accelerated could be related to efferent signals from motor areas predicting the sensory consequences of our actions.

Attention↗
PubMed2006

Noise causes slant underestimation in stereo and motion.

This paper discusses a problem, which is inherent in the estimation of 3D shape (surface normals) from multiple views. Noise in the image signal causes bias, which may result in substantial errors in the parameter estimation. The bias predicts the underestimation of slant found in psychophysical and computational experiments. Specifically, we analyze the estimation of 3D shape from motion and stereo using orientation disparity. For the case of stereo, we show that bias predicts the anisotropy in the perception of horizontal and vertical slant. For the case of 3D motion we demonstrate the bias by means of a new illusory display. Finally, we discuss statistically optimal strategies for the problem and suggest possible avenues for visual systems to deal with the bias.

Form Perception↗
PubMed2006

Feature-based attention influences contextual interactions during motion repulsion.

Visual perception is strongly shaped by the spatial context in which stimuli are presented. Using center-surround configurations with oriented stimuli, recent studies suggest that voluntary attention critically determines which stimuli in the surround affect the percept of the central stimulus. However, evidence for attentional influences on center-surround interactions is restricted to the spatial selection of few among several surround stimuli of different orientations. Here, we extend these insights of center-surround interactions to the motion domain and show that the influence of surround information is critically shaped by feature-based attention. We used motion repulsion as an experimental test tool. When a central target motion was surrounded by a ring of motion, subjects misperceived the direction of the foveal target for particular center-surround direction differences (repulsion condition). Adding an appropriate second motion in the surround counterbalanced the effect, eliminating the repulsion. Introducing feature-based attention to one of the two superimposed directions of motion in the surround reinstated the strong contextual effects. The task relevance of the attended surround motion component effectively induced a strong motion repulsion on the foveally presented stimulus. In addition, the task relevance of the foveal stimulus also induced motion repulsion on the attended surround direction of motion. Our results show that feature-based attention to the surround strongly modulates the veridical perception of a foveally presented motion. The observed attentional effects reflect a feature-based mechanism affecting human perception, by modulating spatial interactions among sensory information and enhancing the attended direction of motion.

Attention↗
PubMed2006

Temporal dynamics of stereo correspondence bi-stability.

Periodic stereoscopic stimuli offer multiple viable solutions to the stereo correspondence problem. When viewing such stimuli for prolonged periods of time, observers continually switch their perceptual state between alternative correspondence solutions. We examine the temporal dynamics of this correspondence bi-stability. Participants were presented with an ambiguous stereogram comprised of regularly spaced dots. This stimulus was perceived as a fronto-parallel plane situated either behind or in front of fixation, depending on the achieved correspondence solution. The stimulus was presented continuously for one minute, with participants instructed to report the sign of the perceived depth at the sound of an auditory prompt presented, on average, every 2 s. Inter-ocular contrast and available disparities were varied so as to manipulate preferred correspondence. We find that participants are initially biased to perceive the stimulus as having an uncrossed disparity. Furthermore, we find that following an initial period of change, perceptual preference and perceptual stability (measured as the probability of an observer's percept changing between consecutive responses) remain constant over the presentation period. Finally, we find that manipulations of matching preference affect both the transient preference for, and stability of, one percept over another. Our results suggest two distinct phases of biasing in the correspondence matching process, one early, the other sustained.

Depth Perception↗
PubMed2006

The utility of surface reflectance for the recognition of upright and inverted faces.

The variation among faces can be partitioned into two sources: (a) shape and (b) surface reflectance. To compare the utility of shape and reflectance for face recognition, we created two sets of faces, with individual exemplars differing only by shape in one set and only by reflectance in the other set. Grayscale and full color versions of the stimuli were used in separate experiments; the physical variation between exemplars was equated across the two sets with the grayscale but not the full color stimuli. Subjects performed a matching task in which both the target and distractor were drawn from the same set, so that only shape or only reflectance information could be used to perform the task. With the grayscale stimuli, performance was better in the shape condition, but with the color stimuli, performance was better in the reflectance condition. Inversion of the faces disrupted performance with the shape and reflectance sets about equally, suggesting that the inversion effect is not caused specifically by the spacing of facial features, or even by shape information more generally. These results provide evidence that facial identity is a function of reflectance as well as shape, and place important constraints on explanations of why inversion impairs face recognition.

Adaptation, Ocular↗
PubMed1995

Decision and attribution bias in neurorehabilitation.

OBJECTIVE: Examine neurorehabilitation therapists' clinical predictions and attributions for outcomes. DESIGN: Single sample, repeated measures. PARTICIPANTS: A sample of 51 neurorehabilitation therapists selected from representative disciplines including occupational therapy, physical therapy, speech therapy, and recreation therapy. MAIN OUTCOME MEASURES: Self-report questionnaire on factors related to positive and negative outcomes in neurorehabilitation. Rank order listing of factors influencing outcome in neurorehabilitation. RESULTS: Without cuing, therapists did not identify injury severity as factor in outcome (p < .0001). Therapists also made internal attributions for positive outcomes and external attributions for negative outcomes (p < .0001). CONCLUSIONS: Neurorehabilitation therapists tend to ignore injury severity as factor in outcome unless encouraged to do so. Therapists accept personal responsibility for positive outcomes, but not for negative outcomes. Neurorehabilitation teams may benefit from education on factors affecting prognosis and attribution bias found in clinical practice.

Adult↗
PubMed1997

Height phobia and biases in the interpretation of bodily sensations: some links between acrophobia and agoraphobia.

The present study was designed to investigate some of the factors that might underlie the commonly found association between agoraphobia and fear of heights (acrophobia). The results showed that measures of acrophobia are highly associated with the tendency to interpret ambiguous bodily sensations as threatening, and with an increased tendency to report bodily sensations of anxiety. These features of acrophobia did not appear to be characteristics found in phobic states in general, nor did measures of acrophobia show any significant relationship to the tendency to interpret external and social stimuli as threatening. These findings suggest that the frequently found co-morbidity between agoraphobia and acrophobia may be linked to cognitive biases in the discrimination and interpretation of bodily sensations that agoraphobia and acrophobia share in common. In addition, the present findings also generate testable hypotheses about the aetiology of acrophobia.

Adolescent↗
PubMed1999

Inflated perceptions of responsibility and obsessive-compulsive symptoms.

In Salkovskis' [Salkovskis, P. (1985). Obsessional-compulsive problems: a cognitive-behavioural analysis. Behaviour Research and Therapy, 28, 571-588; Salkovskis P. (1989) Cognitive-behavioural factors and the persistence of intrusive thoughts in obsessional problems. Behaviour Research and Therapy, 27, 677-682] cognitive model for obsessive-compulsive disorder (OCD), inflated perception of responsibility is highlighted as the critical feature that maintains the disorder. In the current study, the relationship between responsibility and obsessive-compulsive (OC) symptoms was examined. Specifically, three measures of responsibility were evaluated for their psychometric properties. These measures were then used to test Salkovskis's model by examining the relationships among pervasive responsibility, automatic thoughts related to causing harm, and OC symptom severity. Findings provide partial support for the validity and reliability of the measures and for the model as a whole. Based on regression analyses, data support that pervasive responsibility significantly contributes to the prediction of OC symptoms. Furthermore, this relationship appears to be mediated by automatic thoughts related to causing harm in OCD contexts.

Adult↗
PubMed2000

Touch feel illusion in schizophrenic patients.

BACKGROUND: The rubber hand illusion is a tactile sensation referred to as an alien limb. The illusion has been explained by a spurious reconciliation of visual and tactile inputs reflecting functional connectivity in the brain and was used to explore alterations of functional connectivity in schizophrenia. METHODS: The rubber hand illusion was achieved when two paintbrushes simultaneously stroke the hand of the subject hidden from vision by a screen, as well as an artificial hand placed in view of the subject. The rubber hand illusion was assessed with a questionnaire affirming or denying the occurrence of the illusion. RESULTS: Schizophrenic subjects felt the illusion stronger and faster then did normal control subjects. Some rubber hand illusion effects correlated with positive symptoms of schizophrenia but not with negative symptoms. CONCLUSIONS: Altered functional integration of environmental inputs could constitute the basis for erroneous interpretations of reality, such as delusions and hallucinations.

Adult↗
PubMed2001

Prism adaptation of reaching is dependent on the type of visual feedback of hand and target position.

The present study demonstrated that the magnitude of after-effect due to wedge prisms depends on the form of the visual feedback used to represent hand and target position in fast, targeted, transverse reaches. Trained human subjects made reaches with and without prisms in three visuomotor representations (VR): (1) the subject's actual hand and targets (Direct), (2) a real-time video broadcast of hand and targets (Video), or (3) abstract, computer-generated targets and a cursor representing hand position (Cursor). A significant after-effect occurred in each VR. However, the magnitude of the after-effect was significantly different among VRs: the magnitude was greatest in Direct, smaller in Video and smallest in Cursor. A significant after-effect (carryover) also occurred when a subject prism-adapted reaches in one VR and then removed the prisms and made initial reaches in another VR. Our data showed that when reaches were prism-adapted in Direct and then prisms were removed, there was a large carryover to initial reaches in Video or Cursor (D-->V and D-->C). In contrast, when prisms were worn in Video and removed for reaches in Direct (V-->D), there was a significantly smaller carryover than from both D-->V and D-->C. Finally, when prisms were worn in Cursor and removed for reaches in Direct (C-->D), there was very little detectable carryover. Our results suggest that adaptation is context-dependent and that the magnitude of carryover is dependent on the VR in which adaptation occurred. Interpretations of adaptations made in abstract training and experimental conditions may be greatly affected by this finding.

Adaptation, Physiological↗
PubMed1997

Identity and similarity factors in repetition blindness: implications for lexical processing.

The influence of identity and similarity of repeated items on repetition blindness (RB) was investigated in two rapid-serial-visual processing (RSVP) tasks. In Experiment 1, the difference between correct recall for sentences containing repeated identical items and their controls was contrasted with the difference between correct recall for sentences containing pairs of orthographically similar items (fish-dish) and their controls. In Experiment 2 the same comparison was made between sentences containing repeated identical items and sentences containing pairs of orthographically identical items (the watch-to watch). The amount of RB elicited by the two conditions was measured at three different temporal lags. The results show that the function that describes performance over time for the repeated-identical (R-I) condition is different from that for the condition in which the items are orthographically similar (repeated-neighbor: R-N) or orthographically identical (repeated-homonym: R-H). The results are interpreted as suggesting that the decrements in performance observed for recall of the second occurrence of the repeated item in the R-I and the R-N and R-H conditions have different underlying causes.

Analysis of Variance↗
PubMed2002

Seeing happy emotion in fearful and angry faces: qualitative analysis of facial expression recognition in a bilateral amygdala-damaged patient.

Neuropsychological studies reported that bilateral amygdala-damaged patients had impaired recognition of facial expressions of fear. However, the specificity of this impairment remains unclear. To address this issue, we carried out two experiments concerning the recognition of facial expression in a patient with bilateral amygdala damage (HY). In Experiment 1, subjects matched the emotion of facial expressions with appropriate verbal labels, using standardized photographs of facial expressions illustrating six basic emotions. The performance of HY was compared with age-matched normal controls (n = 13) and brain-damaged controls (n = 9). HY was less able to recognize facial expressions showing fear than normal controls. In addition, the error pattern exhibited by HY for facial expressions of fear and anger were distinct from those exhibited by both control groups, and suggested that HY confused these emotions with happiness. In Experiment 2, subjects were presented with morphed facial expressions that blended happiness and fear, happiness and anger, or happiness and sadness. Subjects were requested to categorize these expressions by two-way forced-choice selection. The performance of HY was compared with age-matched normal controls (n = 8). HY categorized the morphed fearful and angry expressions blended with some happy content as happy facial expressions more frequently than normal controls. These findings support the idea that amygdala-damaged patients have impaired processing of facial expressions relating to certain negative emotions, particularly fear and anger. More specifically, amygdala-damaged patients seem to give positively biased evaluations for these negative facial expressions.

Adult↗
PubMedDate not supplied

Comparison of the Milner and Bisiach Landmark Tasks: can neglect patients be classified consistently?

The aim of the presented studies was to investigate whether classifications of neglect patients into perceptual (i.e. identifying a patient as suffering from mainly attentional/space representation deficits) and premotor (judging the main impairment to be related towards actions into contralesional space) categories are consistent across similar Landmark techniques that have, in the past, been designed to tease these potentially overlapping aspects of hemispatial neglect apart. Thirteen patients with hemispatial neglect were tested both with the Landmark Test, adapted from Milner et al. (1992; 1993) in which they had to manually point to the half of a centrally pre-bisected line that, to them, appeared shorter and the motor version of the Bisiach Landmark Test (Bisiach et al., 1998) in which, rather than just judging a centrally prebisected line, they had to judge asymmetrically bisected lines as well. The specific question was whether these two tasks, which are very similar, would categorise the same set of patients in the same way. Most patients could be classified into either the premotor or perceptual category in each task, but no consistent categorisation emerged across the two tests. Just three out of the thirteen patients were consistently classified across both tests. Despite the apparent similarity of the two tests the Milner Landmark Test proved to be much more sensitive to identifying even a slight perceptual bias and seems therefore the test of choice if identification of perceptual bias is the major interest.

Aged↗
PubMedDate not supplied

Prism adaptation and spatial attention: a study of visual search in normals and patients with unilateral neglect.

Visuomotor adaptation to a prism-induced lateral displacement of the visual field induces mild perceptual biases in healthy individuals and improves symptoms of unilateral neglect. The present study employed a speeded visual search task to test the hypothesis that prism adaptation induces an adaptive redistribution of selective spatial attention. In Experiment 1, 32 neurologically healthy, right-handed participants were adapted to a 150 prism-induced lateral (left or right) displacement of the visual field. Spatial attention was measured by search time and error-rate in unique-feature ("preattentive") and feature-absent ("serial") visual search tasks, before and after prism adaptation. The single target appeared at different locations within arrays of 12, 24 or 48 items. Contrary to the attentional hypothesis, the pattern of search performance across the display remained unchanged following prism adaptation. In Experiment 2, we tested four patients with unilateral right hemisphere damage on the visual search tasks, before and after adaptation to 15 degrees rightward-displacing prisms. All four patients showed a pathological gradient of spatial attention toward the ipsilesional side prior to adaptation. Consistent with the results from Experiment 1, the gradient in search performance shown by the patients did not change following prism adaptation. Taken together, these findings suggest that the perceptual aftereffects in normals and amelioration of unilateral neglect following prism adaptation are not mediated by an adaptive redistribution of spatial attention.

Adaptation, Psychological↗
PubMed2002

Visuomotor adaptation to optical prisms: a new cure for spatial neglect?

In this issue, McIntosh and colleagues show that visual and haptic deficits in spatial neglect can be improved following a brief period of visuomotor adaptation to rightward displacing optical prisms. Their paper is the latest in a series of recent studies that have demonstrated the utility of prismatic adaptation in reducing the clinical symptoms of unilateral spatial neglect (Pisella et al., 2002; Rode et al., 1999; Rossetti et al., 1998; Rossetti et al., 1999). The technique has great promise as a rehabilitative tool, and may provide unique insights into the underlying mechanisms of spatial perception and action in normality and pathology. In this article I provide an introduction to the neuropsychological syndrome of spatial neglect, highlighting the significant rehabilitative challenges it poses for clinicians. I then outline the prism adaptation procedure, and consider the possible reasons for its beneficial effects in patients with spatial neglect. I conclude with some open questions and suggestions for future research.

Adaptation, Psychological↗
PubMed2002

Prism adaptation improves chronic visual and haptic neglect: a single case study.

Visuomotor adaptation to rightward displacing optical prisms is known to induce temporary improvements in the symptoms of left visual neglect. We report a 74 year-old woman with severe and chronic neglect of nine months duration, who underwent three weekly sessions of prism adaptation. Substantial improvements were obtained on tests of visual neglect (cancellation, copying and bisection). Improvement was also observed on a spatial judgement task, with no explicit visual component, in which CS was required to locate the centre of a haptically explored circle. These observations confirm that brief periods of prism exposure can benefit even chronic neglect disorders. Moreover, the improvement observed on the haptic task supports the belief that this procedure can influence higher levels of spatial representation.

Aged↗
PubMed1992

Visual agnosia: a case of reduced attentional "spotlight"?

A case study is presented of a patient with presenile dementia, for whom the dominant clinical feature from onset was a visual agnosia. The characteristics of the patient's visual agnosia were investigated in light of her apparent use of a "feature-by-feature" strategy to identify objects. Results from various tasks showed that the patient was unable to use global shape information or other grossly defined property cues characteristic of a "wide angle" attentional processing stage (Treisman, 1988) in object recognition. The patient appeared instead to rely on 'parts' or identifying features of the objects for object recognition. The patient showed significant improvement when the size of the drawing was reduced in size, thus suggesting that the disorder may be functionally localized to a reduction of the patient's attentional "spotlight".

Agnosia↗