Current explanations for the Ames Trapezoid Illusion are based upon the the absence of cues: the illusion is said to occur at chance. A review of recent literature showed that: (a) the illusion varies in frequency as a function of target shape (b) that the dominant cue to reduce the frequency of the illusion is the variant in retinal height. Based upon the dominance of this cue a new model was presented. Following this model it was hypothesized that observers viewing partial rotation when the target produces the greatest difference in the retinal height of the ends would determine the true direction more accurately than observers viewing the same target when the differences in the retinal height was least. The results confirmed the hypothesis.

While various studies have related susceptibility to the Mueller-Lyer illusion to mental health, to developmental maturity, and to self-differentiation, there have been no studies in which susceptibility to the illusion has been related to a wide spectrum of self-concept dimensions. It is one of the purposes of the present study to analyze susceptibility to the Mueller-Lyer illusion as a function of errors in self-perception. To the extent that an individual suffers conflicts with regard to his self-concept, in any of its significant dimensions, it is expected that he will suffer a greater susceptibility to the illusion.

Action has many influences on how and what we perceive. One robust example of the relationship between action and subsequent perception, which has recently received great attention in the cognitive sciences, is the “intentional binding” effect: When people estimate the timing of their actions and those actions’ effects, they judge the actions and effects as having occurred closer together in time than two events that do not involve voluntary action (Haggard, Clark, & Kalogeras, 2002). This dissertation examines the possible mechanisms and consequences of the intentional binding effect. First, in Chapter 1, I discuss previous literature on the relationships between experiences of time, action, and causality. Impressions of time and causality are psychologically related: The perceived timing of events impacts, and is impacted by, perceived causality. Similarly, one’s experience of causing and controlling events with voluntary action, sometimes called the sense of agency, shapes and is shaped by how those events’ timing is perceived—as shown by the intentional binding effect. In Chapter 2 I present a series of experiments investigating a hypothesized mechanism underlying the intentional binding effect: Actions may lead to a slowing of subjective time, which would explain the intentional binding effect by postulating a shorter experienced duration between action and effect. This hypothesis predicts that, following action, durations separating any two stimuli would appear subjectively shorter. We tested this hypothesis in the context of visual motion illusions: Two visual stimuli are presented in short succession and if the duration between the stimuli (inter-stimulus interval; ISI) is short, participants tend to perceive motion such that the first stimulus appears to move to the position of the second stimulus. If actions shorten subjective durations, even in visual perception, people should observe motion at longer ISIs when the stimuli follow voluntary action because the two stimuli would be separated by less subjective time. Three experiments confirmed this prediction. An additional experiment showed that verbal estimates of the ISI are also shorter following action. A control experiment suggested that a shift in the ability to prepare for the stimuli, afforded by the participant initiating the stimuli, is an unlikely alternative explanation of the observed results. In Chapter 3 I further investigate whether temporal contiguity of actions and their effects, which is known to impact intentional binding, affects perceptions of visual motion illusions. Two experiments showed that temporal contiguity modulates perceptions of illusory motion in a manner similar to contiguity’s effect on intentional binding. Together, these results show that actions impact perception of visual motion illusions and suggest that general slowing of subjective time is a plausible mechanism underlying the intentional binding effect.