Impaired peripheral reaching and on-line corrections in patient DF: Optic ataxia with visual form agnosia

Abstract

An influential model of vision suggests the presence of two visual streams within the brain: a dorsal occipito-parietal stream which mediates action and a ventral occipito-temporal stream which mediates perception. One of the cornerstones of this model is DF, a patient with visual form agnosia following bilateral ventral stream lesions. Despite her inability to identify and distinguish visual stimuli, DF can still use visual information to control her hand actions towards these stimuli. These observations have been widely interpreted as demonstrating a double dissociation from optic ataxia, a condition observed after bilateral dorsal stream damage in which patients are unable to act towards objects that they can recognize. In Experiment 1, we investigated how patient DF performed on the classical diagnostic task for optic ataxia, reaching in central and peripheral vision. We replicated recent findings that DF is remarkably inaccurate when reaching to peripheral targets, but not when reaching in free vision. In addition we present new evidence that her peripheral reaching errors follow the optic ataxia pattern increasing with target eccentricity and being biased towards fixation. In Experiments 2 and 3, for the first time we examined DF's on-line control of reaching using a double-step paradigm in fixation-controlled and free-vision versions of the task. DF was impaired when performing fast on-line corrections on all conditions tested, similarly to optic ataxia patients. Our findings question the long-standing assumption that DF's dorsal visual stream is functionally intact and that her on-line visuomotor control is spared. In contrast, in addition to visual form agnosia, DF also has visuomotor symptoms of optic ataxia which are most likely explained by bilateral damage to the superior parietal occipital cortex. We thus conclude that patient DF can no longer be considered as an appropriate single-case model for testing the neural basis of perception and action dissociations.

Actions obey Weber’s law when precision is evaluated at goal attainment

“…In everyday life, pointing is directed toward a wide range of targets, whether in 2D or 3D, such as buttons, switches, and digital elements on screens or tablets. Therefore, the use of digital targets to investigate pointing movements represents a practical and ecologically valid approach, as highlighted by their application in many motor control studies (e.g., Connolly et al, 2003;Diedrichsen et al, 2004;Gentilucci et al, 1996;Hesse et al, 2012Hesse et al, , 2014Pélisson et al, 1986;Rossit et al, 2018).…”

Review: Sport Performance and the Two-visual-system Hypothesis of Vision: Two Pathways but Still Many Questions

“…However, more recent studies show that patient DF's story is not so simple. Some recent studies show her visually guided actions to be highly inaccurate both when controlled by peripheral vision 45,46 and when haptic feedback is removed, 47 with the claim being that she shows damage to both object recognition and action control. Moreover, functional MRI FIGURE 1.…”

“…However, more recent studies show that patient DF's story is not so simple. Some recent studies show her visually guided actions to be highly inaccurate both when controlled by peripheral vision 45,46 and when haptic feedback is removed, 47 with the claim being that she shows damage to both object recognition and action control. Moreover, functional MRI shows patient DF to have damage to her ventral and dorsal streams (e.g., bilateral thinning in the intraparietal sulcus in the dorsal stream in addition to her extensive bilateral ventral stream damage 48,49 ).…”

Grasping Weber’s Law in a Virtual Environment: The Effect of Haptic Feedback

“…In particular, the shaping of the grip aperture is unaffected by tasks-irrelevant, perceptually driven information about objects and their surroundings ( Aglioti et al, 1995 ; Ganel and Goodale, 2003 ; Ganel et al, 2008 ; Chen et al, 2015 ; Namdar et al, 2018 but see Franz and Gegenfurtner, 2008 ; Kopiske et al, 2016 ). These findings have been attributed to the proposed functional separation between visual perception and visual control of action ( Goodale and Milner, 1992 ; Milner and Goodale, 2008 ; but see Glover and Dixon, 2001 ; Smeets and Brenner, 2008 ; Rossit et al, 2018 for different views). These findings have been recently extended to two-hand, bimanual motor control ( Ganel et al, 2017 ; Ozana and Ganel, 2020 ).…”