Abstract
Directing attention based on behavioral relevance and prior expectations about regularities in the environment both impact perceptual decision-making (Summerfield & de Lange, 2014). Some suggest that attention and expectations both impact early sensory processing, whereas others suggest that expectations only influence later stages of decision-making. However, to date, only a few studies have examined these two modulatory factors within the same experiment to determine if they operate via similar or independent mechanisms. In the present study, participants viewed a display containing flickering iso-oriented lines, half of which were blue and half of which were red. On each trial, some percentage of the lines were rendered in the same orientation (forming a ‘coherent’ global orientation). We manipulated attention (behavioral relevance) by cueing participants to monitor either the red or blue lines (focused attention) or to monitor both (divided attention). Expectation of the target-defining coherent orientation was manipulated by varying the probability of a given target orientation within a block of trials. Finally, we examined interactions between stimulus strength and attention/expectation by manipulating the fraction of flickering lines that define the target orientation (low/high coherence). Participants indicated their response using a flight-simulator joystick, while EEG data were recorded. We found that attention modulated EEG signals (the visual negativity and the centro-parietal positivity) by improving sensory encoding and the rate of sensory evidence accumulation in the same manner as increasing stimulus strength. In contrast, expectation selectively modulated EEG markers of the later stages of decision-making including executive control and response selection, without affecting early markers associated with early sensory processing. These results suggest that attention and expectation have a separable impact on decision-making, and that expectation, in the absence of changes in behavioral relevance, does not impact early sensory processing.
Acknowledgement: NEI R01EY025872 and James S. McDonnell Foundation awards to J.T.S., HHMI International Predoctoral Fellowship and a Royal Thai Scholarship from the Ministry of Science and Technology in Thailand to S.I., and mission funding from the U.S. Army Research Laboratory