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Business • Minor grade adjustments on Midterm 2 • Opportunity to participate in Cognitive Neuroscience and Perception experiment - sign up for Tuesday, Wednesday or Thursday afternoons by emailing [email protected] Neural Correlates of Selection • Since attention has a profound effect on perception, one would expect it to have some measurable effect on the brain Neural Correlates of Selection • Since attention has a profound effect on perception, one would expect it to have some measurable effect on the brain • This has been confirmed with a variety of techniques: EEG, fMRI/PET, Unit Recordings Neural Correlates of Selection • Electrical activity recorded at scalp (EEG) shows differences between attended and unattended stimuli in A1 within 90 ms Hansen & Hillyard (1980) Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task MONKEY FIXATES CENTRE CROSS Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task “CUE” APPEARS AT FIXATION Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task DELAY SEVERAL SECONDS Neural Correlates of Selection • Remember that different neurons have a “preference” for different features • Some stimuli excite a given neuron and others do not Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task DELAY SEVERAL SECONDS Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task MONKEY MAKES EYE MOVEMENT TO TARGET Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task • Question: does attention modulate spike rate of neurons that respond to visual stimuli? Neural Correlates of Selection • Remember that different neurons have a “preference” for different features • If a “good” stimulus appears, neurons tuned to the features of that stimulus are initially excited, but remain so only if attention is focused on that stimulus Chellazi et al. (1993). A neural basis for visual search in Inferior Temporal Cortex. Nature. 363, 345-347 Stimulus is distractor Stimulus is target Neural Correlates of Selection • Results: Neurons in visual system respond vigorously to certain stimuli but are then sharply suppressed if a different stimulus is selected by attention Neural Correlates of Selection • Results: Neurons in visual system respond vigorously to certain stimuli but are then sharply suppressed if a different stimulus is selected by attention • Interpretation: this selection is a neural correlate of the perceptual suppression of unattended information Neural Correlates of Selection • Is this a neural correlate of consciousness? Next time: • memory