Attention – Neurophysiology Hillyard’s experiments – dichotic listening: attention-dependent effect on ERP amplitude. Early or late? Study by Woldorff et al., localization of an early (20-50 ms latency) attention effect using ERP(F)/MRI).
07.21 Woodman, G., and Luck, S. (1999). Electrophysiological measurements of rapid shifts of attention during visual search. Nature 400:867.
07.22 Figs. 4, 5, and 6, Corbetta et al., “Selective and divided attention during visual discriminations of shape, color and speed: Functional anatomy by positron emission tomography, The Journal of Neuroscience 11: 2383–2402, (1991) Adapted with permission of The Society for Neuroscience. Adapted from Heinze, H.J., Mangun, G.R., Burchert, W., Hinrichs, H., Scholz, M., Münte, T.G., Gös, A., Scherg, M., Johannes, S., Hundeshagen, H., Gazzaniga, M.S. and Hillyard, S.A., Combined spatial and temporal imaging of brain activity during visual selective attention in humans, Nature 372 (1994): 543–546.
Attention – Neuroimaging Previous imaging studies revealed: changes in neural activity related to attentional shifts (parietal lobe) and attention-related specific activation of extrastriate areas (color, form, motion). No changes in V1 . Recent fMRI studies (e.g. Somers et al., 1999): - Selective visual attention modulates neural activity in extrastriate cortex, as well as in V1 . - Attentional modulations in V1 are spatially specific. - “Window of attention can be spatially complex”, hints at object-selective attention.
Attention – Neuroimaging Flattening of the occipital lobe (Somers et al., 1999)
(a) and (b): Stimulus (c) and (d): Topography (e) and (f): Attentional Modulation
Attention – Top-Down Most “natural” visual scenes are composed of multiple objects. Receptive fields in higher visual areas are large (up to 25 degrees) and typically contain multiple objects at one time. This creates a problem for neurons encoding specific object features…
“ On the side opposite to”: In what frame of reference does neglect occur (space, object, world)?
How do we define LEFT?
Reference Frame: system for representing locations relative to some standard coordinate system
Neglect affects multiple reference frames
Unilateral Neglect: Frames of Reference Neglect patient JM’s copying of a daisy presented in different orientions. Spatial or object-centered?
Unilateral Neglect and Memory Bisiach’s patient (unable to recall half of the piazza del duomo) – representations are affected, not just acute visual input (“unilateral neglect of representational space”)