Disentangling the mechanisms of the boundary restriction effect

Author: Deanne M Green

Green, Deanne M, 2020 Disentangling the mechanisms of the boundary restriction effect, Flinders University, College of Education, Psychology and Social Work

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The role of visual memory is not to make a complete picture of the world, but rather to understand the meaning of what we see so that we can navigate the world. Thus, our visual memory is prone to errors. One such visual memory error is boundary extension, whereby people misremember seeing more of the periphery of a scene than they actually saw. This visual memory error is common and robust. However, the opposite memory error—whereby people remember seeing less periphery of a scene than they actually saw—can also occur. This visual memory error, boundary restriction, seems to occur after viewing negative visual stimuli. However, boundary restriction is not as robust as boundary extension, and some studies have actually failed to find the effect. Few studies have attempted to disentangle the mechanisms behind boundary restriction to determine why it occurs only after viewing some, but not all, negatively valenced stimuli. I seek to address this gap by investigating the possible mechanisms that may induce the boundary restriction effect. More specifically, I investigated a number of possible mechanisms in isolation; specifically, whether boundary restriction could be induced by (1) the presence of negative visual imagery (2) valence in isolation from negative visual imagery (3) attention both in the presence of, and isolated from, negative visual imagery, and (4) arousal in isolation from negative visual imagery.

Overall, my experiments revealed three important findings. First, valence appears to contribute little to inducing boundary restriction errors. I found that both the presence of negative stimuli, and priming ambiguous images to be negatively valenced did not induce boundary restriction. Second, I found that short presentation times and focussed attention induced boundary restriction errors. However, using an incidental measure of attention ––relying on participants’ natural tendency to over-attend to the left hemifield––did not induce boundary restriction. Third, I found that aversive arousal can both induce boundary restriction errors, and decrease boundary extension errors.

My findings may explain why the literature surrounding boundary restriction is so mixed. Boundary restriction seems to occur not due to the negativity of visual stimuli, but rather due to the arousing and/or attention-grabbing nature of the stimuli instead. Thus, I conclude that boundary restriction may be a natural visual memory error, but one that occurs only under specific circumstances, and not one that occurs for all negative visual scenes. Boundary extension remains the more common visual memory error, and is only reversed under specific, highly arousing circumstances. Future research should further test this finding by investigating the way boundary restriction is measured (i.e., investigating different test types) or by employing materials that specifically heighten arousal and capture attention, rather than focussing on negative stimuli to induce the effect.

Keywords: Boundary restriction, boundary extension, visual memory, perception, memory errors

Subject: Psychology thesis

Thesis type: Doctor of Philosophy
Completed: 2020
School: College of Education, Psychology and Social Work
Supervisor: Melanie Takarangi