Abstract: Prospective memory (PM) is the memory for actions to be performed in the future. Laboratory paradigms designed to examine the factors underlying successful prospective memory have typically utilized single element displays; however, such paradigms can’t reflect the real rich environment in which the realization of intentions is embedded. Besides, previous experiments using a limited set of behavioral measures (i.e. accuracy and response time) can not further explore the inner processing mechanisms underlying event-based PM. The current study sought to address this issue by embedding a prospective memory task in a visual search task in which multi-objects would be presented in the display. As a complement to commonly used measures of response time and accuracy, this study examined various indices of eye movement behavior which provided insight into the eye processing and allowed us to observe which factors mainly contributed to the failures of prospective memory—either the failure to focally attend to the prospective cues or the failure to engage strategic process that facilitate the realization of delayed intentions.
18 undergraduates (8 women, 10 men) averagely aged 22.25 years participated as paid volunteers. All participants were healthy, right-handed and had normal or corrected to normal vision. In each trial, individuals were presented with a single letter to encode which served as the target in the trial. The target disappeared after it was encoded and a display of 6 horizontally aligned letters appeared. The ongoing task for participants was to determine whether the target was presented in the display, and when participants saw D or M in the search display, they should press another specific key as the prospective task. There are four conditions in the displays: targets only, prospective cues only, target plus prospective cue, distractors (stimuli that were neither targets nor prospective cues). The quantity of targets and prospective cues were counterbalanced between different conditions. Participants’ eye movements were tracked with German SMI iView X-RED Eye Tracking System. Responses were collected using a 4-button response pad.
The response accuracy data revealed that the ongoing task hits were more frequent than prospective hits, and the response time for prospective cues only as well as distractors was longer than that for targets only. The eye tracking data revealed that there were no differences among all conditions in the quantity of fixations. Both first and total fixation durations increased from distractors to targets to prospective cues. In the failures of prospective memory, the possibility of fixations on the prospective cues largely existed, and the presence of a target in the display served to disrupt the attention to prospective cues. Moreover, individuals tended to look longer at the stimulus which was associated with the response to be made. These findings suggested that the possibility of fixating the prospective cues may not necessarily contribute to the success in prospective memory, and the realization of the intentions need checking and preparatory attentional process for prospective cues, supporting strategic control processing.

Key words: multi-objects, event-based prospective memory, eye tracking, strategic control processing