PS2111 CDL Session 5.pptx

PS2111 The functions of vision Part 1 Carlo De Lillo In previous sessions Pattern and object recognition – Internal representations to enable recognition – Importance of encoding relationship between object parts Mental imagery – Different types of mental representations – Encoding of relationship b...

PS2111 The functions of vision Part 1 Carlo De Lillo In previous sessions Pattern and object recognition – Internal representations to enable recognition – Importance of encoding relationship between object parts Mental imagery – Different types of mental representations – Encoding of relationship between objects in the environments – Mental maps influenced by inferences, assumptions, semantics Visual guidance of action – Rapid reflexive guidance of action via vision – Not influenced by previous knowledge In this session Evidence for different cognitive/neural systems supporting different visual functions Mostly work stemming from by Milner and Goodale’s theory of functions of vision Will start with brief recap of visual systems Primary visual pathways From the retina to the primary visual cortex Cortical visual pathways From primary visual cortex to: Parietal cortex Temporal cortex Dissociation of “what” and “where” systems in the cortex (Ungerlainder & Mishkin, 1982) parietal lesions - dorsal system impairment of spatial information processing e.g. identify location landmark temporal lesions - ventral system impairment of feature processing e.g. identify object regardless of spatial position near Is vision without awareness possible? Cortical blindness - damage of part of primary visual cortex - blindness for corresponding part of visual field Blindsight (Weiskrantz 1986) Patient D.B. Removal of most right primary visual cortex Patient unaware of presence of target in blind portion of visual field Forced trials - direct gaze to target location - point to target location - ability to locate target within blind portion of visual field Traditional explanation of blindsight Intact sub-cortical circuits superior colliculus pulvinar Summary of part 1 Primary visual pathways Cortico-cortical visual pathways What and where: dorsal - ventral dichotomy Bilndsight PS2111 The functions of vision Part 2 Carlo De Lillo Milner & Goodale (1995) Alternative hypothesis about ventral and dorsal functions ventral = “what” system vision for awareness dorsal = “how” system vision for action Core characteristics of the ventral and dorsal processing streams (Schenk and McIntosh, 2010) Ventral stream: vision for perception, produces conscious representations Dorsal stream underlines vision-for-action, reflex-like often not conscious Coding in the ventral stream is allocentric (object-centred; encodes relationship between objects independent observer’s perspective) Coding in dorsal stream is egocentric (body-centred; dependent on observer’s perspective) Representations in the ventral stream are long-lasting, those in the dorsal stream are short-lasting. Processing in the ventral stream typically (but by no means always) leads to conscious awareness, whereas processing in the dorsal stream does not. Neuropsychological evidence Visual agnosia - damage to occipital-temporal cortex (ventral stream) Optic ataxia - damage of posterior parietal cortex (dorsal stream) Neuropsychological evidence Visual agnosia (patient DF) - damage of occipito-temporal complex - inability to recognise objects - almost unimpaired navigational skills Neuropsychological evidence Optic ataxia - damage of posterior parietal cortex - failure to reach accurately for objects - unimpaired recognition of the same objects - difficulty in positioning fingers or adjusting grip Patient D.F. (Goodale et al., 1991) Visual agnosia Inability to recognise size, shape and orientation of visual objects Poor shape recognition of real objects Spared tactual recognition Presented with blocks of different dimensions – unable to distinguish between them – unable to indicate their width Asked to reach for the blocks – able to scale her grip appropriately Re-assessment of DF suggests more cautious conclusion (Hillbach et al 2012) further analyses of DF’s performance based on original data by Goodale et al. (1994) compared to 20 new healthy controls DF’s performance on the grasping task inferior to that of controls However, general pattern of results confirmed Other dissociations in DF Failure to report the orientation of the slot Failure to match the orientation of a target Able to insert a card into the slot Dissociation between perception for awareness and perception for action in non-clinical groups (e.g. Carey, 2001) Perception for awareness size illusion Perception for action grip not affected by illusion Perceiving and grasping the Muller-Lyer illusion (Haart et al. 1999) 3D version of illusion Matching task indicate length with index and thumb Grasping task rapidly grasp shaft with index and thumb Meta-analyses of literature on visual illusions in relation to Milner and Goodale’s proposal show that effects are not always as strong as originally believed but in general support the theory (e.g. Bruno et al. 2008) Actions guided by memory involvement the ventral stream (Milner et al. 2003). Two patients with optic ataxia (damage to the dorsal stream) Reaching and grasping movements - immediately - a few seconds after the offset of the target object Patients’ performance better in memory condition Patients do better in the memory condition as they use their intact ventral stream Unconscious visual guidance of reaching obstacle-avoidance task (McIntosh et al. (2004) neuropsychological patient VE stroke damage to right hemisphere impaired conscious awareness stimuli in his left visual field in the presence of a stimulus in right visual field (symptom know as extinction) VE able to avoid a rod obstacle in left visual field even when unable to consciously see it reaching influenced by visual information which was not conscious Target reaching area Fixation Obstacles Summary Part 1 Primary visual pathways Cortico-cortical visual pathways What and where: dorsal - ventral dichotomy Part 2 What and how dichotomy: dorsal - ventral dichotomy reinterpreted vision for perception vs action Clinical neuropsychological evidence for the vision for perception/action theory - Visual agnosia - Optic ataxia - Extinction Experimental evidence - Illusions Reading Essential - Bruce, Green and Georgeson, Visual Perception, Chapter 3, pp. 57-69 - Eysenck & Keane, Cognitive Psychology (2015, 7th ed.) , Chapter 2, pp. 48-56; 71-80 Recommended - Norman 2002. Two visual systems and two theories of perception: an attempt to reconcile the constructivist and ecological approaches. Behavioral and Brain Sciences, 25-73-144 - Milner, A.D. & Goodale, M.A. (2008) Two visual systems reviewed. Neuropsychologia, 46: 774-785.