Electrophysiology of Visual Attention

1. Electrophysiology of Visual Attention

2. Intracranial Recordings of Attentional Selection • Moran and Desimone (1985) • “Classical” RF prediction: there should be no difference in responses in these two conditions

3. Intracranial Recordings of Attentional Selection • Moran and Desimone (1985) • Result: Response to “Sample” Response to “Sample” Response to Target Response to Target “effective” stimulus at unattended location “effective” stimulus at attended location

4. Intracranial Recordings of Attentional Selection • Moran and Desimone (1985) • Result: • Neuron responds vigorously only if its effective stimulus is attended • Interesting caveat: this only applies when there is an ineffective stimulus (to which the monkey attends) present in the V4 RF • When the ineffective stimulus is outside of the cell’s RF, its responses are largely unmodulated

5. Intracranial Recordings of Attentional Selection • What about the time course of this attention effect? • Are cells modulated in advance by the cue? • Or are they modulated by attention when it is shifted to the target location? • What is needed is a experiment design such that the monkey orients attention after the target appears

6. Intracranial Recordings of Attentional Selection • Chellazi et al ( 1993) Neural Correlates of Visual Search • Monkey is trained in a delayed match-to-sample task • Cue appears 1.5 seconds before search array • Monkey saccades to target • “good” and “poor” stimuli are identified for each recorded neuron

7. Intracranial Recordings of Attentional Selection • Note that monkey isn’t “pre-cued” to attend to a location • Only target features are known prior to choice array onset • With this paradigm it is possible to measure cell activity during delay, during search, and after selection • Note that search array always contains a “good” stimulus for the recorded cell – but that might not be the target

8. Intracranial Recordings of Attentional Selection • Initial response of cells is “classical”

9. Intracranial Recordings of Attentional Selection • Initial response of cells is “classical” • Response during delay maintains a representation of the target feature

10. Intracranial Recordings of Attentional Selection • Initial response of cells is “classical” • Response during delay represents the target feature • Initial response to search array is “classical”

11. Intracranial Recordings of Attentional Selection • About 200 ms after array onset response of cell begins to depend on attention • Response becomes more vigorous if cell is tuned to features of the target (i.e. the selected stimulus) • Response becomes suppressed if cell is tuned to a non-target distractor

12. Intracranial Recordings of Attentional Selection • Conclusion: • Attentional selection of locations and/or objects has physiological correlates and consequences • How does attention get to where it needs to go?