Abstract
Patients with simultanagnosia, which is a component of Bálint syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a time. As a result, these patients see the world in a piecemeal fashion, seeing the local components of objects or scenes at the expense of the global picture. To directly test the relationship between the restriction of the attentional window in simultanagnosia and patients’ difficulty with global-level processing, we used a gaze-contingent display to create a literal restriction of vision for healthy participants while they performed a global/local identification task. Participants in this viewing condition were instructed to identify the global and local aspects of hierarchical letter stimuli of different sizes and densities. They performed well at the local identification task, and their patterns of inaccuracies for the global level task were highly similar to the pattern of inaccuracies typically seen with simultanagnosic patients. This suggests that a restricted spatial area of visual processing, combined with normal limits to visual processing, can lead to difficulties with global-level perception.
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Notes
Patients with Bálint syndrome present with dorsal (as opposed to ventral) simultanagnosia (Farah 1990), which is an attentional limitation that prevents patients from seeing more than one object at a time. Thus, we define simultanagnosia in this context strictly as a reduction in attentional processing capacity that is in part reflected by a failure to process or maintain attention to a larger region of the visual field outside of the current focus of attention, as opposed to the more general definition offered by Wolpert (1924), which also includes difficulty with the interpretation of the global concept of a scene or a figure.
We do not to report reaction times (RTs) because patient SL’s responses were entered by the experimenter and are therefore unreliable. The gaze-contingent group had long trial durations, whereas the full-view group responded almost instantly; hence, any differences in RTs for these groups are relatively uninformative.
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Acknowledgments
KD was supported by the Natural Sciences and Engineering Research Council (NSERC), and the Michael Smith Foundation for Health Research (MSFHR). WB was supported by NSERC. JB was supported by a Canada Research Chair and MSFHR Senior Scholarship. AK was supported by grants from NSERC, the Social Sciences and Humanities Research Council, and the Canadian Institutes for Health Research. Thank you to SL for time and dedication to this project.
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Dalrymple, K.A., Bischof, W.F., Cameron, D. et al. Simulating simultanagnosia: spatially constricted vision mimics local capture and the global processing deficit. Exp Brain Res 202, 445–455 (2010). https://doi.org/10.1007/s00221-009-2152-3
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DOI: https://doi.org/10.1007/s00221-009-2152-3