Attention - Overview

Definition

Theories of Attention

Neural Correlates of Attention•Human neurophysiology and neuroimaging

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Deficits of Attention•Unilateral neglect

Stroop Task

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Stroop Task

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Stroop Task

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Stroop

• Failure of selective attention

• Race model– Word name is processed automatically

– Color is not so automatic

– Both arrive at the same time, we have a hard time attending to the relevant stimulus attribute

– Doesn’t happen upside down

Stroop Task.

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).

W. W. Norton

W. W. Norton

W. W. Norton

Woodman, G., and Luck, S. (1999). Electrophysiological measurements of rapid shifts of attention during visual search. Nature 400:867.

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…

Attention – Top-Down

Ambiguous response

Attention – Top-Down

Ambiguity in neural response can be reduced by:

a) Referencing spatial (retinal) location

b) Attentional modulation of firing rate

Attention – Top-Down

Prediction

Un-ambiguous response

W. W. Norton

W. W. Norton

Moran and Desimone, 1985

Note: visual input does not change (fixation point), what changes is the focus of covert attention

Cellular Basis of Attention

Unilateral Neglect

Unilateral Neglect

Eye movements from a patient with left unilateral neglect, during visual exploration

Hemineglect

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Unilateral Neglect: Frames of Reference

“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”)

What Causes Unilateral Neglect?

1. Neglect results from damage to the attentional orienting system. Attention is mostly deployed to the right.

2. Neglect is caused by a failure to construct a complete mental representation of contralesional space.

Change Blindness

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Change Blindness Applet

Change Blindness Applet

Salience Model

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