Biology subjects

Burlingham, C. S.

Publications and source records attributed to Burlingham, C. S..

6 recordsLinked to original sources

bioRxiv2023

Motor "laziness" constrains fixation selection in real-world tasks

AO_SCPLOWBSTRACTC_SCPLOWPeople coordinate their eye, head, and body movements to gather information from a dynamic environment while maximizing reward and minimizing biomechanical and energetic costs. Such natural behavior is not possible in a laboratory setting where the head and body are usually restrained and the tasks and stimuli used often lack ecological validity. Therefore, its unclear to what extent principles of fixation selection derived from lab studies, such as inhibition-of-return (IOR), apply in a real-world setting. To address this gap, participants performed nine real-world tasks, including driving, grocery shopping, and building a lego set, while wearing a mobile eye tracker (169 recordings; 26.6 hours). Surprisingly, spatial and temporal IOR were absent in all tasks. Instead, participants most often returned to what they just viewed, and saccade latencies were shorter preceding return than forward saccades. We hypothesized that participants minimize the time their eyes spend in an eccentric position to conserve eye and head motor effort. Correspondingly, we observed center biases in the distributions of fixation location and duration, relative to the heads orientation. A model that generates scanpaths by randomly sampling these distributions reproduced the spatial and temporal return phenomena seen in the data, including distinct 3-fixation sequences for forward versus return saccades. The amount of the orbit used in each task traded off with fixation duration, as if both incur costs in the same space. Conservation of effort ("laziness") explains all these behaviors, demonstrating that motor costs shape how people extract and act on relevant visual information from the environment. Significance StatementHumans display remarkably precise yet flexible control of eye and body movements, allowing for a wide range of activities. However, most studies of gaze behavior use the same setup: a head-restrained participant views small images on a computer. Such lab studies find that people avoid looking at the same thing twice, and hesitate in cases when they do. We had people perform nine everyday activities while wearing glasses with embedded eye tracking, and surprisingly found that they did the opposite, often returning to what they just viewed and expediting these "return" eye movements over others. A tendency to keep the eyes centered in the head, which we speculate helps to conserve motor effort, explained these behaviors for all tasks.

neuroscience↗

bioRxiv2022

Perceptual learning improves discrimination while distorting appearance

Perceptual sensitivity often improves with training, a phenomenon known as perceptual learning. Another important perceptual dimension is appearance, the subjective sense of stimulus magnitude. Are training-induced improvements in sensitivity accompanied by more accurate appearance? Here, we examine this question by measuring both discrimination and estimation capabilities for near-horizontal motion perception, before and after training. Human observers who trained on either discrimination or estimation exhibited improvements in discrimination accuracy alongside increased biases in their estimates away from horizontal. To explain this counterintuitive finding, we developed a computational observer model in which perceptual learning arises from increases in the precision of underlying neural representations. For each observer, the fitted model accounted for both discrimination performance and the distribution of estimates, and their changes after training. Our empirical findings and modeling suggest that learning enhances distinctions between categories, a potentially important aspect of real-world perception and perceptual learning.

neuroscience↗

bioRxiv2021

Task-related hemodynamic responses in human early visual cortex are modulated by task difficulty and behavioral performance

Early visual cortex exhibits widespread hemodynamic responses in the absence of visual stimulation, which are entrained to the timing of a task and not predicted by local spiking or local field potential (LFP). Such task-related responses ("TRRs") covary with reward magnitude and physiological signatures of arousal. It is unknown, however, if TRRs change on a trial-to-trial basis according to behavioral performance and task difficulty. If so, this would suggest that TRRs reflect arousal on a trial-to-trial timescale and covary with critical task and behavioral variables. We measured fMRI-BOLD responses in the early visual cortex of human observers performing an orientation discrimination task consisting of separate easy and hard runs of trials. Stimuli were presented in a small portion of one hemifield, but the fMRI response was measured in the ipsilateral hemisphere, far from the stimulus representation and focus of spatial attention. TRRs scaled in amplitude with task difficulty, behavioral accuracy, reaction time, and lapses across trials. These modulations were not explained by the influence of respiration, cardiac activity, or head movement on the fMRI signal. Similar modulations with task difficulty and behavior were observed in pupil size. These results suggest that TRRs reflect arousal and behavior on the timescale of individual trials.

neuroscience↗

bioRxiv2021

A unified model of the task-evoked pupil response

The pupil dilates and re-constricts following task events. It is popular to model this task-evoked pupil response as a linear transformation of event-locked impulses, the amplitudes of which are used as estimates of arousal. We show that this model is incorrect, and we propose an alternative model based on the physiological finding that a common neural input drives saccades and pupil size. The estimates of arousal from our model agreed with key predictions: arousal scaled with task difficulty and behavioral performance but was invariant to trial duration. Moreover, the model offers a unified explanation for a wide range of phenomena: entrainment of pupil size and saccade occurrence to task timing, modulation of pupil response amplitude and noise with task difficulty, reaction-time dependent modulation of pupil response timing and amplitude, a constrictory pupil response time-locked to saccades, and task-dependent distortion of this saccade-locked pupil response.

neuroscience↗

bioRxiv2019

Uncharacteristic task-evoked pupillary responses implicate atypical locus coeruleus activity in autism

Autism spectrum disorder (ASD) is characterized partly by atypical attentional engagement, such as hypersensitivity to environmental stimuli. Attentional engagement is known to be regulated by the locus coeruleus (LC). Moderate baseline LC activity globally dampens neural responsivity and is associated with adaptive deployment and narrowing of attention to task-relevant stimuli. In contrast, increased baseline LC activity enhances neural responsivity across cortex and widening of attention to environmental stimuli regardless of their task relevance. Given attentional atypicalities in ASD, this study is the first to evaluate whether individuals with ASD exhibit a different profile of LC activity compared to typically developing controls under different attentional task demands. Males and females with ASD and age- and gender-matched controls participated in a one-back letter detection test while task-evoked pupillary responses--an established inverse correlate for baseline LC activity--were recorded. Participants completed this task in two conditions, either in the absence or presence of distractor auditory tones. Compared to controls, individuals with ASD evinced atypical pupillary responses in the presence versus absence of distractors. Notably, this atypical pupillary profile was evident despite the fact that both groups exhibited equivalent task performance. Moreover, between-group differences in pupillary responses were observed only in response to task-relevant and not to task-irrelevant stimuli, providing confirmation that the group differences are specifically associated with distinctions in LC activity. These findings suggest that individuals with ASD show atypical modulation of LC activity with changes in attentional demands, offering a possible mechanistic and neurobiological account for attentional atypicalities in ASD. Significance StatementIndividuals with autism spectrum disorder (ASD) exhibit atypical attentional behaviors, such as environmental hypersensitivity and atypical fixedness, but the neural mechanism underlying these behaviors remains elusive. One candidate mechanism is atypical locus coeruleus (LC) activity, as the LC has a critical role in attentional modulation. Elevated LC activity is associated with environmental exploration, while moderate LC activity is associated with focused attention on relevant stimuli. This study shows that, under tightly controlled conditions, task-evoked pupil responses--an LC activity proxy--are lower in individuals with ASD than in controls, but only in the presence of task-irrelevant stimuli. This suggests that individuals with ASD evince atypical modulation of LC activity in accordance with changes in attentional demands, offering a mechanistic account for attentional atypicalities in ASD.

neuroscience↗

bioRxiv2018

Heading Perception Depends on Time-Varying Evolution of Optic Flow

There is considerable support for the hypothesis that perception of heading in the presence of rotation is mediated by instantaneous optic flow. This hypothesis, however, has never been tested. We introduce a novel method, termed "non-varying phase motion," for generating a stimulus that conveys a single instantaneous optic flow field, even though the stimulus is presented for an extended period of time. In this experiment, observers viewed stimulus videos and performed a forced choice heading discrimination task. For non-varying phase motion, observers made large errors in heading judgments. This suggests that instantaneous optic flow is insufficient for heading perception in the presence of rotation. These errors were mostly eliminated when the velocity of phase motion was varied over time to convey the evolving sequence of optic flow fields corresponding to a particular heading. This demonstrates that heading perception in the presence of rotation relies on the time-varying evolution of optic flow. We hypothesize that the visual system accurately computes heading, despite rotation, based on optic acceleration, the temporal derivative of optic flow.

neuroscience↗