Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Faculty/School

Faculty of Science

First Advisor

Philip Servos

Advisor Role

Dissertation Supervisor

Abstract

The tactile motion aftereffect (tMAE) is a perceptual phenomenon in which illusory motion is reported following adaptation to a unidirectionally moving tactile stimulus. Unlike its visual counterpart, relatively little is known about the tMAE. For that reason, the purpose of this dissertation was to gain a better understanding of the tMAE using both psychophysical and neuroimaging techniques. In a series of five experiments the skin was adapted using a plastic cylinder with a square-wave patterned surface. Chapter 2 consists of two experiments, both of which adapted the glabrous surface of the right hand. Experiment 1 showed that the prevalence, duration, and vividness of the tMAE did not differ between the fingers (thumb excluded), palm and fingers (thumb included), and palm and fingers (thumb excluded). Thus, the divergent prevalence rates of two previous studies (Hollins & Favorov, 1994; Lerner & Craig, 1994) cannot be explained by the inclusion of the thumb in the latter study. Experiment 2 showed that as adapting speed increased from 15 to 75 rpm so did the prevalence, duration, and vividness of the tMAE. Previously it has been shown that the tMAE duration increases with adapting duration (Hollins & Favorov, 1994). Given that speed * duration = distance, increasing either adapting speed or duration also increases distance. As such, it was unclear which parameter(s) caused the observed increase in prevalence, duration, and vividness. Chapter 3 manipulated adapting duration (1, 2, and 4 min) and speed (30 and 60 rpm) in the same experiment, thereby allowing the effect of distance to be assessed in the interaction. The results showed that the prevalence, duration, and vividness of the tMAE increased with adapting speed. There was also a positive relationship between adapting duration and prevalence, but not duration or vividness, of the illusion. Distance was only a factor when it came to the tMAE duration. To gain insight into the peripheral neural basis of the tMAE, Chapter 4 measured the prevalence, duration, and vividness of the tMAE on skin areas that differ in their composition of fast adapting (FA) mechanoreceptive units, namely the right cheek, volar surface of the forearm, and glabrous surface of the hand. While there was no difference in duration or vividness between the skin surfaces tested, the tMAE was reported twice as often on the hand than the cheek and forearm, which did not differ significantly from one another. This finding suggests that the tMAE can be induced by adapting FA type I (FA I) units in the glabrous skin (hand) and the hair follicle units (cheek and forearm) and/or the FA I (cheek) and field (forearm) units in the hairy skin. Chapter 5 investigated the central neural basis of the tMAE using functional magnetic resonance imaging (fMRI). Of the areas shown to be responsive to tactile motion on the glabrous surface of the right hand, namely the contralateral (left) thalamus, postcentral gyrus (PCG), and parietal operculum, only the PCG showed evidence of the tMAE; that is, there was a sustained fMRI response following the offset of the illusion trials (cylinder rotating at 60 rpm), but not the control trials (cylinder rotating at 15 rpm), presumably reflecting illusory motion perception. Taken together, the experiments described herein expand our knowledge of the tMAE. Using a cylinder adapting apparatus, it was shown that: prevalence is the best measure of tMAE strength; the tMAE is not as robust as its visual counterpart; adapting duration and speed positively affect the prevalence of the tMAE; the tMAE is twice as prevalent on the glabrous than the hairy skin; the FAI and hair follicle units likely underlie the tMAE; the tMAE is likely caused by adapting direction selective neurons in the contralateral PCG.

Convocation Year

2009

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