1. Theoretical Models of Attention

2. Broadbent (1958) conceptualized attention as information processing Used a cuing paradigm to show that attentional selection of one channel dramatically biased perception Believed that unattended inputs were filtered out altogether x x xx oo o o o

3. 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

4. Early Selection Early Selection model failed to explain some findings Shadowing studies found that certain information could “intrude” into the attended stream – Subject’s name, loud noises, etc.

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

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

7. Electrophysiological Investigations of Attention

8. Modulation of Auditory Pathways The theory is that attention acts as an early selection filter The prediction is that selective auditory attention modulates early responses in the auditory pathway Hernandez-Peon (1956) – Electrodes in cats – Attended tones elicited more rapid spike trains What was the critical confound?

9. Modulation of Auditory Pathways Failed to rule out overt orienting – Cats can orient their ears without moving their heads – Not surprising that auditory responses went up when cat swiveled its ears Solution was to careful monitor subject’s orienting with eye trackers and present stimuli through headphones

10. Modulation of Auditory Pathways Hillyard et al. (1960s) 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 attending LEFT Ignoring RIGHT

11. 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

12. 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 – ERP effects may reflect recurrent rather than feed forward processes