Biomedical subjects

Leanne Boucher

Publications and source records attributed to Leanne Boucher.

4 recordsLinked to original sources

PubMed2006

Influence of history on saccade countermanding performance in humans and macaque monkeys.

The stop-signal or countermanding task probes the ability to control action by requiring subjects to withhold a planned movement in response to an infrequent stop signal which they do with variable success depending on the delay of the stop signal. We investigated whether performance of humans and macaque monkeys in a saccade countermanding task was influenced by stimulus and performance history. In spite of idiosyncrasies across subjects several trends were evident in both humans and monkeys. Response time decreased after successive trials with no stop signal. Response time increased after successive trials with a stop signal. However, post-error slowing was not observed. Increased response time was observed mainly or only after cancelled (signal inhibit) trials and not after noncancelled (signal respond) trials. These global trends were based on rapid adjustments of response time in response to momentary fluctuations in the fraction of stop signal trials. The effects of trial sequence on the probability of responding were weaker and more idiosyncratic across subjects when stop signal fraction was fixed. However, both response time and probability of responding were influenced strongly by variations in the fraction of stop signal trials. These results indicate that the race model of countermanding performance requires extension to account for these sequential dependencies and provide a basis for physiological studies of executive control of countermanding saccade performance.

Animals↗

PubMed2004

Smooth pursuit under stimulus-response uncertainty.

Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRT and CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming joystick tracking but not for smooth pursuit eye movements (SPEMs).

Adult↗

PubMed2002

Saccades operate in violation of Hick's law.

Hick's law states that response times (RTs) increase in proportion to the logarithm of the number of potential stimulus-response (S-R) alternatives. We hypothesized that time-consuming processes associated with response selection contribute significantly to this effect. We also hypothesized that the latency of saccades might not conform to Hick's law since visually guided saccades can be automatically selected using topographically organized pathways that convert spatially coded visual activity into spatially coded motor commands. We evaluated these hypotheses by examining three response modalities for their compliance with Hick's law: saccades directed to a visual target (prosaccades), saccades directed away from the target (antisaccades) and manual responses in which each digit was associated with a specific target location (key-press responses). Both antisaccades and key-press responses conformed to Hick's law but saccade latencies were completely unaffected by S-R uncertainty. The significance of these findings is considered in terms of the processes of response selection and premotor programming.

Humans↗

PubMedDate not supplied

Ocular tracking as a measure of auditory motion perception.

Motion is a potent sub-modality of vision. Motion cues alone can be used to segment images into figure and ground and break camouflage. Specific patterns of motion support vivid percepts of form, guide locomotion by specifying directional heading and the passage of objects, and in case of an impending collision, the time to impact. Visual motion also drives smooth pursuit eye movements (SPEMs) that serve to stabilize the retinal image of objects in motion. In contrast, the auditory system does not appear to be particularly sensitive to motion. We review the ambiguous status of auditory motion processing from the psychophysical and electrophysiological perspectives. We then report the results of two experiments that use ocular tracking performance as an objective measure of the perception of auditory motion in humans. We examine ocular tracking of auditory motion, visual motion, combined auditory + visual motion and imagined motion in both the frontal plane and in depth. The results demonstrate that ocular tracking of auditory motion is no better than ocular tracking of imagined motion. These results are consistent with the suggestion that, unlike the visual system, the human auditory system is not endowed with low-level motion sensitive elements. We hypothesize however, that auditory information may gain access to a recently described high-level motion processing system that is heavily dependent on 'top-down' influences, including attention.

Acoustic Stimulation↗