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-o- topy, 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.