In four experiments we used eye-tracking to investigate biases in looking behaviour during visual decision making tasks. In Experiment 1, participants viewed arrays of images of photographic art and decided which image was preferred (from a set of either two or eight alternatives). To analyze gaze behaviour during the decision we identified dwells (where a dwell is a series of consecutive fixations on a decision alternative). This analysis revealed two forms of gaze bias in the period prior to the response. Replicating prior findings (Shimojo, Simion, Shimojo, & Scheier, 2003), just prior to the response we found an increase in the frequency of dwells on the chosen item. In addition, throughout the decision, dwells on the chosen item were longer than dwells on other items. This pattern of biases was extremely similar across preference and non-preference decision instructions, but overall the biases were more pronounced in eight alternative decisions than in two alternative decisions. In Experiment 2 we manipulated the number of decision alternatives while controlling for differences in the stimulus displays. Participants viewed displays containing six everyday items, and chose either which of two sets of three items was the most expensive (two alternative set selection task) or which of the six items was the most expensive (six alternative item selection task). Consistent with Experiment 1, participants exhibited greater selectivity in their processing of stimulus information in the six alternative decisions compared to the two alternative decisions. In Experiments 3 and 4 we manipulated stimulus exposure in order to test predictions derived from the Gaze Cascade model (Shimojo et al., 2003). In Experiment 3, participants performed an eight alternative decision in which four of the items had been pre-exposed prior to the decision. In Experiment 4, stimulus exposure was manipulated during the ongoing decision using a gaze-contingent methodology. While these manipulations of stimulus exposure had strong effects on gaze bias, the specific predictions of the model were not supported. Rather, we suggest an interpretation based on prior research, according to which the gaze bias reflects the selective processing of stimulus information according to its relevance to the decision task.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/24756 |
| Date | 12 August 2010 |
| Creators | Glaholt, Mackenzie Gavin |
| Contributors | Reingold, Eyal M. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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