Development of a light-emitting diode tachistoscope to investigate the mere exposure effect

The mere exposure effect refers to the phenomenon that the simple repeated, unreinforced exposure to a stimulus enhances affective evaluations towards that stimulus. This preference for familiarity has typically been investigated in relation to meaningless stimuli, with application to real world objects a relatively neglected area. The primary aim of the research described in this thesis was to examine the mere exposure effect to everyday objects. Interestingly, the effect has been found in instances where conscious recognition of the stimuli was precluded, with some suggestion that the effects produced by subliminal stimuli are stronger than those produced by stimuli that are clearly recognized. To clarify the role of exposure duration in the exposure-affect relationship, therefore, a second aim was to compare subliminal versus supraliminal effects. It was found that existing methods of rapid visual stimulus delivery are unreliable at delivering stimuli at rapid durations. A new apparatus, a light-emitting diode (LED) tachistoscope, was constructed and verified as capable of accurately and reliably displaying visual images at durations as rapid as 1 ms. The brief presentation time is afforded by a liquid crystal display (LCD) that is illuminated externally by a brief LED flash after LCD steady-state is reached, such that image onset and offset timing can be precisely controlled. To validate this equipment on a human sample, a visual animal identification task was performed. The unexpected finding emerged that participants were able to successfully identify animals by name 89 % of the time with only 1 ms of exposure. In a follow-on mere exposure study, participants were repeatedly exposed to pictures of polygons for either 1 ms or 1000 ms. These ‘old’ stimuli were then presented again, together with similar but never-before-seen ‘new’ equivalents, and each stimulus was rated for liking and recognition. The mere exposure effect was found for 1000 ms stimuli, with old stimuli receiving significantly higher liking and recognition ratings than new. At 1 ms, old stimuli were liked more than new; however, the difference was not significant. Unexpectedly, even with the more difficult task demand of the mere exposure study, at 1 ms old stimuli received significantly higher recognition ratings than new. Thus, contrary to past research, the 1 ms stimuli were not actually subliminal. The procedure was repeated for pictures of real world objects, namely chairs. This time, at both 1000 ms and 1 ms, old stimuli were liked more than new, providing evidence that the mere exposure effect typically displayed for meaningless stimuli also extends to meaningful stimuli. Again, at both 1000 ms and 1 ms, old stimuli were also rated significantly higher for recognition than new. The unexpected recognition performance from both the animal and mere exposure studies was attributed to iconic memory and top-down, feedback cortical processing. The findings not only indicate that the visual system is more efficient at extracting information than previously thought, but they also seriously challenge the concept of subliminality, thus calling into question the findings of existing subliminal mere exposure studies. Furthermore, the LED tachistoscope opens up new avenues for visual perceptual research and provides a means for uncovering the limits of human visual perception.