Hisato IMAI

The subliminal mere exposure effect is a psychological phenomenon where people tend to prefer stimuli that they have been subliminally exposed to even if they cannot recognize the observed stimuli. One explanation for this effect is that the resulting perceptual fluency is misattributed to a feeling of preference. Thus, an increased perceptual fluency should correspond to decreased invested mental effort. Because the pupil constricts as mental effort decreases, we predict that if perceptual fluency does induce a preference for the exposed stimulus, then participants showing pupil constriction during subliminal exposure will exhibit the mere exposure effect later. To examine our hypothesis, we measured the pupil diameter while participants were visually exposed to subliminal stimuli. After exposure, participants judged their preferences to the stimuli. We found that pupil diameter during subliminal exposure was significantly smaller for participants who later exhibited the mere exposure effect, suggesting that perceptual fluency may be the underlying mechanism of the subliminal mere exposure effect.

This study examines whether the involuntary recollection of an autobiographical memory elicited from an odor cue is determined by cue identifiability, emotional valence, or frequency of everyday encounters. After a semantic-differential (SD) task for various odors, participants (N=74) were asked about occurrences of involuntary recollections during the SD task. The results revealed that more frequently encountered odors were more likely to trigger involuntary recollections. However, no effects were observed for identifiability or emotional valence. These findings suggest that odor cues induce involuntary recollections in a non-verbal manner and that the process of involuntary recollection varies according to cue type.

We investigated whether audiovisual synchrony perception for speech could change after observation of the audiovisual temporal mismatch. Previous studies have revealed that audiovisual synchrony perception is re-calibrated after exposure to a constant timing difference between auditory and visual signals in non-speech. In the present study, we examined whether this audiovisual temporal recalibration occurs at the perceptual level even for speech (monosyllables). In Experiment 1, participants performed an audiovisual simultaneity judgment task (i.e., a direct measurement of the audiovisual synchrony perception) in terms of the speech signal after observation of the speech stimuli which had a constant audiovisual lag. The results showed that the "simultaneous" responses (i.e., proportion of responses for which participants judged the auditory and visual stimuli to be synchronous) at least partly depended on exposure lag. In Experiment 2, we adopted the McGurk identification task (i.e., an indirect measurement of the audiovisual synchrony perception) to exclude the possibility that this modulation of synchrony perception was solely attributable to the response strategy using stimuli identical to those of Experiment 1. The characteristics of the McGurk effect reported by participants depended on exposure lag. Thus, it was shown that audiovisual synchrony perception for speech could be modulated following exposure to constant lag both in direct and indirect measurement. Our results suggest that temporal recalibration occurs not only in non-speech signals but also in monosyllabic speech at the perceptual level.

In this article, we report on an experimental investigation of the spontaneous, uncued recall of prospective memories (memories for activities to be performed at a later time). Einstein & McDaniel (1990) developed an experimental paradigm for investigating prospective memory, in which participants were required to perform both an ongoing task (e.g., remembering words presented on the PC screen) and a prospective memory task (e.g., pressing a designated key whenever they saw a particular word, such as rake). They also claimed that there are two types of prospective memory: one is event-based prospective memory recall, which is triggered by another event ("I will give a message to John when I meet him"), and the other is time-based prospective memory recall, which is to be done after a particular period of time has elapsed (I will call Mary in 30 minutes") or at a certain time ("I will watch TV at 7:00 PM"). We examine the nature of the Einstein and McDaniel's paradigm and show that several important aspects of prospective memory have been left unstudied; specifically, spontaneous, uncued recall. We consider that it is caused by the cue-oriented nature of the paradigm. Furthermore, considering the prospective memory function in our everyday life, we cast doubt of the validity of the dissociation between time-based and event-based prospective memory. To investigate these two issues, we conducted a task-content oriented experiment which was a refined version of Einstein and McDaniel's paradigm. Thirteen undergraduates (9 male and 4 female) were presented 4 photographs on the PC screen simultaneously, and were required to judge which one of these four belonged to a different category (ongoing task). They were also required to stop the ongoing task when a photograph of envelopes was presented during the ongoing task and to call the experimenter in order to answer a questionnaire in an envelope before the experiment finished. Six participants were randomly assigned to an uncued condition, in which the photograph of envelopes was not actually presented (a photograph of a compass was presented instead) and 7 participants to a cued condition. The result showed that, although the expected recall cue was not presented, all the participants in uncued condition spontaneously remembered the prospective memory task. Furthermore, it was revealed that spontaneous recall did not occur randomly; instead, it frequently occurred near the end of the ongoing task, which is similar to the U-shaped clock-checking curve in the time-based prospective memory research (Ceci et al., 1988). These results suggest that participants in the uncued condition performed their event-based prospective memory task as a time-based one, and support our claim that prospective memory has both a time-based and event-based nature.

We conducted a visual search experiment in which participants detected a target (a moving natural image) which moves in the opposite direction to the other distractor images. A set size effect, that is, decrease of accuracy as the number of stimuli in the display increased, was observed. In another experiment to identify a factor that restricted the participants' performance in the task, we used moving random-dot patterns having various amount of relative motion. We found that a target with zero relative motion did pop-out, but the accuracy decreased as the amount of relative motion increased. We estimated the strength of the relative motion of the moving natural images based on the motion-energy model, and found a negative correlation between the accuracy and the strength of relative motion in the natural images. These results suggest that the relative motion is the primary factor for a visual search of moving natural images based on direction information.