A Vertical Asymmetry in Saccades

Visual exploration of natural scenes imposes demands that differ between the upper and the lower visual hemifield. Yet little is known about how ocular motor performance is affected by the location of visual stimuli or the direction of a behavioural response. We compared saccadic latencies between upper and lower hemifield in a variety of conditions, including short-latency prosaccades, long-latency prosaccades, antisaccades, memory-guided saccades and saccades with increased attentional and selection demand. All saccade types, except memory guided saccades, had shorter latencies when saccades were directed towards the upper field as compared to downward saccades (

A World Unglued: Simultanagnosia As A Spatial Restriction Of Attention

Simultanagnosia is a disorder of visual attention that leaves a patient’s world unglued: scenes and objects are perceived in a piecemeal manner. It is generally agreed that simultanagnosia is related to an impairment of attention, but it is unclear whether this impairment is object- or space-based in nature. We first consider the findings that support a concept of simultanagnosia as deficit of object-based attention. We then examine the evidence suggesting that simultanagnosia results from damage to a space-based attentional system, and in particular a model of simultanagnosia as a narrowed spatial window of attention. We ask whether seemingly object-based deficits can be explained by space-based mechanisms, and consider the evidence that object processing influences spatial deficits in this condition. Finally, we discuss limitations of a space-based attentional explanation

Cross-orientation transfer of adaptation for facial identity is asymmetric: A study using contrast-based recognition thresholds

AbstractRecent studies suggest that adaptation effects for face shape and gender transfer from upright to inverted faces more than the reverse. We investigated whether a similar asymmetry occurred for face identity, using a recently developed adaptation method based on contrast-recognition thresholds. When adapting and test stimuli shared the same orientation, aftereffects were similar for upright and inverted faces. When orientation differed, there was significant transfer of aftereffects from upright adapting to inverted test faces, but none from inverted to upright faces. We show that asymmetric cross-orientation transfer of face aftereffects generalize across two distinct face adaptation paradigms: the previously used perceptual-bias methodology and the recently introduced contrast-threshold based adaptation paradigm. These results also represent a generalization from aftereffects for face shape and gender to aftereffects for face identity. While these results are consistent with the dual-mode hypothesis, they can also be accounted for by a single population of units of varying orientation selectivity

“A room full of strangers every day”: the psychosocial impact of developmental prosopagnosia on children and their families

Objective: Individuals with developmental prosopagnosia (‘face blindness’) have severe face recognition difficul¬ties due to a failure to develop the necessary visual mechanisms for recognizing faces. These difficulties occur in the absence of brain damage and despite normal low-level vision and intellect. Adults with developmental prosopagnosia report serious personal and emotional consequences from their inability to recognize faces, but little is known about the psychosocial consequences in childhood. Given the importance of face recognition in daily life, and the potential for unique social consequences of impaired face recognition in childhood, we sought to evaluate the impact of developmental prosopagnosia on children and their families. Methods: We conducted semi-structured interviews with 8 children with developmental prosopagnosia and their parents. A battery of face recognition tests was used to confirm the face recognition impairment reported by the parents of each child. We used thematic analysis to develop common themes among the psychosocial experiences of the children and their parents. Results: Three themes were developed from the child reports: 1) awareness of their difficulties, 2) coping strat¬egies, such as using non-facial cues to identify others, and 3) social implications, such as discomfort in, and avoid¬ance of, social situations. These themes were paralleled by the parent reports and highlight the unique social and practical challenges associated with childhood developmental prosopagnosia. Conclusion: Our findings indicate a need for increased awareness and treatment of developmental prosopagnosia to help these children manage their face recognition difficulties and to promote their social and emotional wellbein

Unilateral Right Parietal Damage Leads to Bilateral Deficit for High-Level Motion

AbstractPatients with right parietal damage demonstrate a variety of attentional deficits in their left visual field contralateral to their lesion. We now report that patients with right lesions also show a severe loss in the perception of apparent motion in their “good” right visual field ipsilateral to their lesion. Three tests of attention were conducted, and losses were found only in the contralesional fields for a selective attention and a multiple object tracking task. Losses in apparent motion, however, were bilateral in all cases. The deficit in apparent motion in the parietal patients supports previous claims that this relatively effortless percept is mediated by attention. However, the bilateral deficit suggests that the disruption is due to a bilateral loss in the temporal resolution of attention to transient events that drive the apparent motion percept

Response Monitoring, Repetitive Behaviour and Anterior Cingulate Abnormalities in Autism Spectrum Disorders (ASD)

Autism spectrum disorders (ASD) are characterized by inflexible and repetitive behaviour. Response monitoring involves evaluating the consequences of behaviour and making adjustments to optimize outcomes. Deficiencies in this function, and abnormalities in the anterior cingulate cortex (ACC) on which it relies, have been reported as contributing factors to autistic disorders. We investigated whether ACC structure and function during response monitoring were associated with repetitive behaviour in ASD. We compared ACC activation to correct and erroneous antisaccades using rapid presentation event-related functional MRI in 14 control and ten ASD participants. Because response monitoring is the product of coordinated activity in ACC networks, we also examined the microstructural integrity of the white matter (WM) underlying this brain region using diffusion tensor imaging (DTI) measures of fractional anisotropy (FA) in 12 control and 12 adult ASD participants. ACC activation and FA were examined in relation to Autism Diagnostic Interview-Revised ratings of restricted and repetitive behaviour. Relative to controls, ASD participants: (i) made more antisaccade errors and responded more quickly on correct trials; (ii) showed reduced discrimination between error and correct responses in rostral ACC (rACC), which was primarily due to (iii) abnormally increased activation on correct trials and (iv) showed reduced FA in WM underlying ACC. Finally, in ASD (v) increased activation on correct trials and reduced FA in rACC WM were related to higher ratings of repetitive behaviour. These findings demonstrate functional and structural abnormalities of the ACC in ASD that may contribute to repetitive behaviour. rACC activity following errors is thought to reflect affective appraisal of the error. Thus, the hyperactive rACC response to correct trials can be interpreted as a misleading affective signal that something is awry, which may trigger repetitive attempts at correction. Another possible consequence of reduced affective discrimination between error and correct responses is that it might interfere with the reinforcement of responses that optimize outcomes. Furthermore, dysconnection of the ACC, as suggested by reduced FA, to regions involved in behavioural control might impair on-line modulations of response speed to optimize performance (i.e. speed-accuracy trade-off) and increase error likelihood. These findings suggest that in ASD, structural and functional abnormalities of the ACC compromise response monitoring and thereby contribute to behaviour that is rigid and repetitive rather than flexible and responsive to contingencies. Illuminating the mechanisms and clinical significance of abnormal response monitoring in ASD represents a fruitful avenue for further research

Training face perception in developmental prosopagnosia through perceptual learning

Background: Recent work has shown that perceptual learning can improve face discrimination in subjects with acquired prosopagnosia. Objective: In this study, we administered the same program to determine if such training would improve face perception in developmental prosopagnosia.Method: We trained ten subjects with developmental prosopagnosia for several months with a program that required shape discrimination between morphed facial images, using a staircase procedure to keep training near each subject’s perceptual threshold. To promote ecological validity, training progressed from blocks of neutral faces in frontal view through increasing variations in view and expression. Five subjects did 11 weeks of a control television task before training, and the other five were re-assessed for maintenance of benefit 3 months after training. Results: Perceptual sensitivity for faces improved after training but did not improve after the control task. Improvement generalized to untrained expressions and views of these faces, and there was some evidence of transfer to new faces. Benefits were maintained over three months. Training also led to improvements on standard neuropsychological tests of short-term familiarity, and some subjects reported positive effects in daily life.Conclusion: We conclude that perceptual learning can lead to persistent improvements in face discrimination in developmental prosopagnosia. The strong generalization suggests that learning is occurring at the level of three-dimensional representations with some invariance for the dynamic effects of expression

The Localization and Patterns of Dyschromatopsia: A Study of Prosopagnosic Subjects (.pdf)

Dyschromatopsia can accompany acquired prosopagnosia, but given the structural variety of the latter, it is not clear which lesions are associated with colour impairments, or whether these impairments also occur with developmental prosopagnosia. In addition, whether the impairment selectively affects specific regions of colour space is uncertain, given conflicting reports in prior single cases

Perception of Global Facial Geometry in the Inversion Effect and Prosopagnosia

We investigated how efficiently combinations of positional shifts in facial features were perceived and whether the effects of combinations on the overall geometry of the face were reflected in discriminative performance. We moved the eyes closer together or further apart, and moved the mouth up or down. Trials with combinations of changes to both the mouth and the eyes were contrasted with trials with single changes to either the mouth or the eyes. As a contrast, we also examined combinations of changes in eye colour (brightness) and the same spatial manipulations. In addition, we specifically contrasted spatial combinations that more severely distorted the original triangular relation of the mouth and eyes (e.g. eyes closer and mouth down) to those that better preserved the original aspect ratio (e.g. eyes farther and mouth down). This we termed the geometric context effect . We found that combinations of two spatial changes were detected more quickly and accurately by normal subjects viewing upright faces but not when faces were inverted. In contrast, combinations of spatial shifts and eye colour changes showed no advantage over faces with only one type of change. Combinations of spatial changes that distorted overall facial geometry more were detected more efficiently than less distorting combinations, showing that the spatial shifts were perceived in the context of the global facial structure. Again, this was found for upright but not inverted faces. We also tested a prosopagnosic patient, who showed the advantage for two spatial changes over one but lacked this geometric context effect, implying that she did not integrate local spatial information into overall facial structure