Consequences of Attentional Selection Single unit recordings

Consequences of Attentional Selection Selection of one location or object or auditory stream has consequences for sensory responses evoked by that stimulus – ERP responses in auditory and visual cortex Are there effects of attentional selection observable at the cellular level? – This is going to require intracranial recordings – What animal would you choose?

Intracranial Recordings of Attentional Selection Moran and Desimone (1985) Recall that: – Cells in ventral stream pathway are selective for color, orientation, complex shapes – “classical” notion of RF is that a cell should fire actively whenever its preferred stimulus is present in its RF – V4 RFs are a few degrees of visual angle – much larger than the resolution of attention What happens when attention selects an object in a cell’s RF if that cell isn’t “tuned” to the features of the object?

Moran and Desimone (1985) – Response properties of cells are identified a priori – Each cell is characterized by what is an “effective” and “ineffective” stimulus – Monkeys were trained to attend to one of several locations within a V4 RF – Monkey is given a target in a delayed match-to- sample task – Respond when target stimulus occurs at cued location Intracranial Recordings of Attentional Selection

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

Moran and Desimone (1985) Result: Intracranial Recordings of Attentional Selection Attend “effective” stimulusAttend “ineffective” stimulus Target Response

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, it’s responses are largely unmodulated 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 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 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

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

Intracranial Recordings of Attentional Selection Initial response of cells is “classical” Response during delay represents the target feature

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”

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 distracter

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?

Orienting Spatial Attention Corbetta et al. (1993) – Subjects oriented attention according to a light moving in the visual field

Orienting Spatial Attention Results: – Parietal and Pre-motor areas were activated by attention tracking task – Hemisphere of activation depended on which visual field attention was being shifted in

Orienting Spatial Attention Corbetta et al (1993) confounded stimulus w/ orienting Hopfinger et al. (2000) used event-related fMRI to identify top-down orienting processes (distinct from stimulus-driven processes) – Cue-target paradigm using arrows – What is the brain activity caused by the cue?

Orienting Spatial Attention Result: – Cue-related activations indicate a distributed network that mediates voluntary orienting – Network includes mainly frontal and parietal structures Orienting to LeftOrienting to Right