Read this article for Friday

1. Read this article for Friday [1]Chelazzi L, Miller EK, Duncan J, Desimone R. A neural basis for visual search in inferior temporal cortex. Nature 1993; 363: 345-347.

2. Attention as Information Selection • consider a simple visual scene:

3. Attention as Information Selection • What if the scene and task gets more complex: “Point to the red vertical line”? • What has to happen in order for this task to be accomplished?

4. Point to Waldo

5. Attention as Information Selection • One conceptualization of attention is that it is the process by which irrelevant neural representations are disregarded (deemphasized? suppressed?) • Another subtly different conceptualization is that attention is a process by which the neural representations of relevant stimuli are enhanced (emphasized? biased?)

6. Attention as Information Selection • These ideas apply to other modalities • auditory “Cocktail Party” problem • somatosensory “I don’t feel my socks” problem

7. Early Selection • Early Selection model postulated that attention acted as a strict gate at the lowest levels of sensory processing • Based on concept of a limited capacity bottleneck

8. Late Selection • Late Selection models postulated that attention acted on later processing stages (not sensory)

9. Early Selection • Early Selection model was intuitive and explained most data but failed to explain some findings • Shadowing studies found that certain information could “intrude” into the attended stream • Subject’s name, loud noises, etc.

10. Late vs. Early • Various hybrid models have been proposed • Early attenuation of non-attended input • Late enhancement of attended input

11. Electrophysiological Investigations of Attention

12. Modulation of Auditory Pathways attending LEFT Ignoring RIGHT • Hillyard et al. (1960s) showed attention effects in human auditory pathway using ERP • Selective listening task using headphones • Every few minutes the attended side was reversed • Thus they could measure the brain response to identical stimuli when attended or unattended beep beep beep beep boop beep beep beep beep boop beep beep

13. Modulation of Auditory Pathways • Result: ERP elicited by attended and unattended stimuli diverges by about 90ms post stimulus • Long before response is made • Probably in primary or nearby auditory cortex

14. Modulation of Auditory Pathways • Other groups have found ERP modulation even earlier – as early as Brainstem Auditory Response • Probably no robust modulation as low as cochlea • by ~40 ms, feed forward sweep is already well into auditory and associated cortex • Thus ERP effects may reflect recurrent rather than feed forward processes

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

16. Intracranial Recordings of Attentional Selection In Vision • Moran and Desimone (1985) • Result: Response to “Sample” Response to “Sample” Response to Target Response to Target “effective” stimulus at unattended location – attention spotlight has selected object with features to which this neuron is not tuned “effective” stimulus at attended location – attention spotlight has selected object with features to which this neuron is tuned

17. Intracranial Recordings of Attentional Selection in Vision • 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