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Try and forget this image: The role of stimulus duration in directed forgetting for natural scenes

Author: Patrick Ihejirika | Advisor: Matt Crump

Undergraduate Honor’s Thesis submitted in partial fulfillment of the requirements for graduating with Departmental Honors in Psychology.

NOTE: This project is currently under development and will be completed in Spring 2022


How useful would it be for you to selectively forget events that you choose to forget? Directed forgetting research is a tool used to investigate limitations on deliberate forgetting abilities. In a directed forgetting task people encode individual items and are instructed (cued) to either remember or forget them. A directed forgetting effect is observed when performance on a memory test is higher for remember-cued items than forget-cued items. Directed forgetting effects have been reproduced numerous times, and are commonly demonstrated in tasks using lists of words as the items to be remembered and forgotten (Epstein, 1969). Much less is known about directed forgetting for more memorable stimuli like images, pictures, and visual scenes. Ahmad, Tan & Hockley showed that a weak directed forgetting effect can in fact be observed for image stimuli (2019).

This honors thesis project investigates a general memory strength hypothesis of directed forgetting for pictures. According to this hypothesis, pictures are difficult to intentionally forget because they are encoded so well that attempts to forget the information are ineffective. I propose that weakening the encoding strength of images could allow intentional forgetting processes to operate more effectively, causing an increased directed forgetting effect. My experiments used the same general procedures as Ahmad, Tan, and Hockley (2019). In two experiments (n=45 each), I reduced encoding strength by manipulating stimulus duration during encoding (2000 ms [original amount], 1000ms, or 500 ms per picture). I predicted that greater directed forgetting would be observed as stimulus duration decreased. I discuss the results of my two experiments in relation to the general memory strength hypothesis.

Project Information and repository notes

The goal of this project repository is to share Patrick Ihejirika’s honor thesis project as a computationally reproducible vertical project.

The purpose of the thesis was to determine whether directed forgetting for pictures would be influenced by changes to decreases in encoding time (stimulus duration) for pictures presented during the encoding phase of recognition memory task.

The honors thesis is available in pdf form from the manuscript tab. The supplementary materials tab contains our power analysis, and results from two experiments.

In theory this entire project is shared in a computationally reproducible format. The github repository for this website contains all of the source code for generating the thesis, the original data, the data analysis, and the experiment scripts used to run the experiment.