Biology subjects

Moreland, J. C.

Publications and source records attributed to Moreland, J. C..

4 recordsLinked to original sources

bioRxiv2021

Oculomotor freezing tracks perception and is immune to decision bias

The appearance of a salient stimulus rapidly inhibits saccadic eye movements. Curiously, this "oculomotor freezing" reflex is triggered only by stimuli that the observer reports seeing. It remains unknown, however, if oculomotor freezing is linked to the observers sensory experience, or their decision that a stimulus was present. To dissociate between these possibilities, we manipulated decision criterion via monetary payoffs and stimulus probability in a detection task. These manipulations greatly shifted observers decision criteria but did not affect the degree to which microsaccades were inhibited by stimulus presence. Moreover, the link between oculomotor freezing and explicit reports of stimulus presence was stronger when the criterion was conservative rather than liberal. We conclude that the sensory threshold for oculomotor freezing is independent of decision bias. Provided that conscious experience is also unaffected by such bias, oculomotor freezing is an implicit indicator of sensory awareness. New & NoteworthySometimes a visual stimulus reaches awareness, and sometimes it does not. To understand why, we need objective, bias-free measures of awareness. We discovered that a reflexive freezing of small eye movements indicates when an observer detects a stimulus. Furthermore, when we biased observers decisions to report seeing the stimulus, the oculomotor reflex was unaltered. This suggests that the threshold for conscious perception is independent of the decision criterion and is revealed by oculomotor freezing.

neuroscience↗

bioRxiv2020

Divided attention for feature-based selection in visual cortex

Feature-based attention can select relevant features such as colors or directions of motion from the visual field irrespective of the spatial position. In visual cortex not only do we see feature-specific attention affecting responses in neurons with receptive fields at an attended location, but that effect also spreads to neurons with receptive fields beyond the spatially relevant location. When only one feature is task relevant, the spread of activity across space can act to facilitate perception of behaviorally relevant stimuli. However, when multiple features are relevant, what is the effect on behavior and brain activity? We tested this question by having observers divide attention between two patches (left and right of fixation) of moving dot stimuli, each containing overlapping upward and downward motion fields. In one condition, subjects performed a task on motion fields moving in the same direction in both patches. In another condition attention was divided between opposite directions of motion. Replicating a previous behavioral study, we found that observers showed better performance when dividing attention to the same directions of motion than opposing directions of motion. We analyzed the BOLD responses while observers performed this task using an inverted encoding model approach that provides estimates of responses to each of the four component dot fields. We found larger responses to the attended components, replicating previous studies of spatial and feature-based attention. However, these effects were much larger when attention was divided to between the same directions of motion than to opposing directions. Our fMRI results in area hMT+ predict our behavioral results by extending the normalization model of attention to include a global feature-based attention component in that leads to suppressed responses to attended stimulus components when attention is directed to opposing directions of motion.

neuroscience↗

bioRxiv2020

Set-size effects in change detection depend on failures of retrieval and/or comparison and not on perception, encoding or storage

Set-size effects in change detection is often used to investigate the capacity limits of dividing attention. Such capacity limits have been attributed to a variety of processes including perception, memory encoding, memory storage, memory retrieval, comparison and decision. In this study, we investigated the locus of the effect of increasing set size from 1 to 2. To measure purely attentional effects and not other phenomena such as crowding, a precue was used to manipulate relevant set size and keep the display constant across conditions. The task was to detect a change in the orientation of 1 or 2 Gabor patterns. The locus of the capacity limits was determined by varying when observers were cued to the only stimulus that was relevant. We began by measuring the baseline set-size effect in an initial experiment. In the next experiment, a 100% valid postcue was added to test for an effect of decision. This postcue did not change the set-size effects. In the critical experiments, a 100% valid cue was provided during the retention interval between displays, or only one stimulus was presented in the second display (local recognition). For both of these conditions, there was little or no set-size effect. This pattern of results was found for both hard-to-discriminate stimuli typical of perception experiments and easy-to-discriminate stimuli typical of memory experiments. These results are consistent with capacity limits in memory retrieval, and/or comparison. For these set sizes, the results are not consistent with capacity limits in perception, memory encoding or memory storage. Significance SectionThe change detection paradigm is often used to demonstrate effects of divided attention. But it is not clear whether these effects are due to perception, memory, or judgment and decision. In this article, we present new evidence that the divided attention effect in change detection is due to limits in memory retrieval or comparison processes. These results are not consistent with limits in perception, memory encoding or memory storage.

animal behavior and cognition↗

bioRxiv2018

Attention explores space periodically at the theta frequency

Voluntary attention is at the core of cognitive functions. Attention can be sustained at a location, or reoriented in space to allow processing at other locations, critical in an ever-changing environment. Numerous studies have investigated attentional orienting in time and space but little is known about the spatio-temporal dynamics of attentional reorienting. Here, we explicitly manipulated attentional reorienting using a cueing procedure in a 2-AFC orientation discrimination task. At various delays during the task, we interrogated attentional deployment by flashing two probe stimuli. Then, solving a second-degree equation to estimate the report probability at each probe location, we demonstrated that attention reorients periodically at ~4 Hz (theta) between the two stimulus locations. We further observed that each stimulus location is sampled at ~11 Hz (alpha). Finally, we support our mathematical approach using simulations and show that this method is sufficiently powered making it a valuable tool for studying the spatio-temporal dynamics of attention.

neuroscience↗