Visuospatial Processing and the Right Hemisphere Interpreter P.M. Corballis Presented by: Cristina, Holly, and Sophie

Bit of History Broca’s Area –Language Production Wernicke’s Ares –Language Comprehension

John Hughlings Jackson  Challenged the notion of left hemisphere dominance instead both hemispheres process specialized abilities.  “Imperception” or visual neglect associated with damage to right hemisphere.  Asymmetrical Lobe Development

Callosotomy Surgery The surgical sectioning of he corpus callosum and in some cases other forebrain commissures Experiments from split- brain patients from the 1960’s supported the notion of left-hemisphere dominance, however, non-verbal test showed right hemisphere activity

Classic Split Brain Research

Left Hemisphere Interpreter Confabulation –when a split-brain patient makes perceptual interpitations The interpreter Ganzzaniga explains Confabulation as evidence for an interpreter that elaborates perceptual information to create a (cohesive) “story” or schema to make sense of the world

Left Hemisphere Domination Language Better fine motor control Superior cognitive abilities?

Vision in the Right Hemisphere Line Drawing Block Design Visual-Spatial Tasks

Studies Mirror Image Left vs Right Hemisphere

Visual System Early Information Redundant processing Asymmetries

Visual Perception as an Intelligent Process Visual system allows us to navigate and interact with the world Problem: 3-D world, 2-D retinal image von Helmholtz: visual perception is top- down as well as bottom up –Retinal image –Experience and goals Hoffman: visual “problem solving”

Visual Perception as an Intelligent Process Low-level: data-driven –No conscious awareness of stimulus High-level: abstract/experience-driven –Phenomenon of visual perception

Is there a Right Hemisphere Interpreter? So far, data indicates that: –“Intelligent” aspects of visual processing are high-level processes –High-level processes are more likely lateralized than low-level processes Hemispheric asymmetry can be viewed as an asymmetry in visual intelligence

Is there a Right Hemisphere Interpreter? 2 experiments showing asymmetry in visual processing –Kanizsa Square –Illusory Line Motion

Kanizsa Square “Modal Completion” Both hemispheres are capable of completing the illusion

Kanizsa Square “Amodal Completion” Contour must be inferred Right hemisphere is better at this illusion

Illusory Line Motion

Both hemispheres influenced by flashing dot Right hemisphere more likely to be influenced by a match in width or color Equivalent to cognitive errors of left hemisphere?

Questions and Further Research They attribute certain aspects of the illusions to a “higher-level” processing –fMRI in normal or split brain subjects –Should see lateralized activity in the parietal and temporal lobe Does the idea of a right-hemisphere interpreter provide an evolutionary advantage?