Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Goodale, Melvyn A.

2nd Supervisor

Corneil, Brian D.



In time-sensitive situations, orienting reflexes allow us to move rapidly in response to stimuli. The express sensorimotor response (ESR) is an orienting reflex presenting as a brief burst of muscle recruitment. Previous studies have identified commonalities between ESRs and express saccades, another orienting reflex.

In this study, we investigate if ESRs share in a characteristic of express saccades: preference for faces. In separate blocks, participants were instructed to reach toward one of two simultaneously appearing targets: a face and another image. Muscle activity in the pectoralis major muscle of the reaching arm was recorded using skin surface EMGs.

We found that the ESR, occurred in greater amplitude towards the instructed target, regardless of whether the instructed target was a face or not. While we found no evidence that ESRs preferer faces, our surprising finding demonstrates that ESRs can be modified by top-down modulation to identify stimulus features based on instruction.

Summary for Lay Audience

In time-sensitive situations, we rely on fast reflexes to respond in a short amount of time. This study investigates the express sensorimotor response (ESR), a reflex that happens in the body muscles when something suddenly comes into our view. More specifically, we investigate if ESRs are more likely to happen if a person sees a face, since faces are more likely to cause other reflexes. To investigate, we instructed participants to reach toward one of two suddenly appearing images: a face and another image.

We found that an ESR occurred within 80ms in all situations. The ESR was stronger in the direction of the instructed target to direct the arm towards it, regardless of whether the instructed target was a face or not. Thus, while we found no evidence that the ESR prefers faces, we surprisingly found that the ESR can respond to a wider range of images than we expected.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.