Transcript Document
A human parietal face area contains aligned head-centered visual and tactile maps Sereno & Huang (2006) • Topographic relationship between position of sensory receptor and position of neuron in grey matter sheet – Superior parietal cortex – Somatosensory position on face – Visual positions close to face – Alignment of the two topographies – Is the visual topography independent of eye position? • Do we calculate a visual map of the world with eye position subtracted? • Such a map might influence our perception Retinotopy - eccentricity Retinotopy – polar angle Transforming between topographies from different modalities • The origin of the auditory sensory space is the head • The origin of visual sensory space is the fovea • Superior colliculus contains an auditory map converted to have a visual sensory origin (retinotopic) – Enables saccades to auditory targets – LIP in parietal cortex is similar • Colour on diagram changes with polar angle • These colours are “mapped” onto cortex • Air puff locations correspond to visual locations Summary of main conditions • Air puff left face versus right face • Air puff polar angle mapping (eyes shut or fixate central) • Visual polar angle map using rotating wedge of “Xena movie” (fixate central) – No reason given why simpler stimulus is inappropriate – 100 deg field of view – why? – Depth cues indicate near visual stimulus for correspondance to facial location (no distant control) • Was it really necessary? – This matches some monkey work – But other studies on “human VIP” use distant optic flow and assign the function of heading perception – VIP may well be VIP+ • Visual polar angle map “Xena” (eyes track stimulus) 25 deg • Face puffs activate S1 and superior parietal focus • Structured motion activates occipital plus superior parietal focus • Alignment of somatotopy and retinotopy • Single subject • Polar angle maps • Alignment good or not so good? • Alignment index? • Average of 9 subjects • Top two views dorsolateral • Bottom view lateral • How good is the alignment? “Gaze-o-topy” • Does this exist? – Is there any systematic periodic response to the circular diagram I showed earlier? • If it does exist, is it aligned in the cortex with the somatotopic (air puff) map? 1 shown (but only 2 in total) Reasonable alignment Tabulated alignment between different mapping experiments Not clear what the alignment index measures Why does the correlation not always agree with the index? Only 2 subjects for gaze-otopy, and one of those has low correlation Possible roles for the gaze independent map of visual space • Sereno – Approaching and manipulating objects with the face • If we consider the VIP+ heading tradition (CUBIC scanner studies!) – Detects collisions under conditions of linear self and object motion via the simple cue that the collision event will not move location on the map, whereas other objects will – And gives the incoming trajectory of the collision enabling its avoidance – Can this be done with retinal flow patterns confounded by eye movement? Verdict? • Gaze independent visual maps would potentially be useful, and could also be a mechanism for visual stability. • However, the evidence presented here is weak, and there is much more data about the reverse remapping process, e.g. superior colliculus.