Biomedical subjects

Akihiro Yagi

Publications and source records attributed to Akihiro Yagi.

5 recordsLinked to original sources

PubMed2003

Information flow related to visual search assessed using magnetoencephalography.

The sequence of neural activation during a visual search task was investigated using magnetoencephalography and the source locations for the activations were analyzed using a single-dipole algorithm. Five components (M1-5) were detected at mean latencies of 110, 146, 196, 250 and 333 ms in both of two different stimulus conditions; a target popped out in one stimulus condition (pop-out), while it did not in the other condition (non-pop-out). Statistical analysis showed that the M3 amplitude was larger and the M5 latency was shorter in the pop-out condition than in the non-pop-out condition, while there was no difference in the other components between the conditions. Neural sources were localized in the calcarine sulcus (M1) and the posterior fusiform gyrus (M2) of the hemisphere contralateral to the stimuli, the intraparietal sulcus and the posterior superior temporal sulcus (M3) in either of the hemispheres, and the calcarine sulcus (M4) of the same hemisphere in which the early processing (M1 and M2) occurred. The criteria for source localization were not satisfied for M5. The results suggest that the processing for pop-out and non-pop-out stimuli share a common mechanism; after early feature processing in the occipital cortex (M1 and M2), visual information is processed in the parietal and temporal regions (M3) and then some of this information is fed back to the occipital cortex (M4).

Adult↗

PubMed2003

Comparison between the lambda response of eye-fixation-related potentials and the P100 component of pattern-reversal visual evoked potentials.

The purpose of this study was to compare the lambda response of eye-fixation-related potentials (EFRPs) with the P100 component of pattern-reversal visual-evoked potentials. EFRPs were obtained by averaging EEGs time-locked to the offset of the saccade. The dipole of the lambda response and that of the P100 component were estimated by the dipole-tracing method (Musha & Homma, 1990). The locations of their dipoles at the occipital sites were very close to each other when the difference waveform, which was calculated by subtracting the EFRP to the patternless stimulus from the EFRP to the patterned stimulus, was used for the lambda response. This finding implies that the lambda response and P100 have a common neural generator in the visual cortex. However, the peak latency of the lambda response was shorter than that of P100. The saccades in the EFRP trial were considered to be the cause of the difference.

Adult↗

PubMed2002

Global interference: the effect of exposure duration that is substituted for spatial frequency.

In this study, participants were required to identify hierarchically structured patterns that appeared at either global or local level. Paquet and Merikle (1984 Canadian Journal of Psychology 381 45-53) showed that global interference is affected by exposure duration in the processing of a hierarchical structure. They showed that only global-to-local interference occurred at short exposure durations. In contrast, global-to-local as well as local-to-global interference was observed at long exposure durations. They suggested that the effect of exposure duration with global interference depends on the high-spatial-frequency versus low-spatial-frequency channel. In the present study, exposure duration (short or long) was varied randomly from trial to trial (experiment 1), or held constant (experiment 2). In experiment 1, global-to-local interference occurred at both short and long exposure durations, even though the same physical properties existed as in experiment 2. In experiment 2, both global-to-local and local-to-global interference occurred at only long exposure durations, in line with the results reported by Paquet and Merikle. This suggests that the effect of exposure duration on global interference is explained not only by spatial-frequency channels, but also by attentional shift.

Computer Graphics↗

PubMed2002

The difference between flipping strategy and spinning strategy in mental rotation.

Murray (1997 Memory & Cognition 25 96-105) showed that, when an inverted object was mentally rotated to upright, the reaction time (RT) of flipping strategy (rotating in depth about the horizontal axis) was shorter than that of spinning strategy (rotating in the picture plane). We hypothesised the absence of representation at the intermediate position between the inverted and the upright representations in the flipping strategy, and investigated this hypothesis by a priming paradigm that included prime and probe tasks within one trial. In the prime task, participants were asked to mentally rotate an inverted object to upright. In the probe task, they were asked to judge whether two objects simultaneously presented were the same or different. The flipping strategy in the prime task did not prime the probe task, whereas the spinning strategy did. The present results suggest that there is no intermediate representation in the flipping strategy: the difference in RT between the flipping strategy and the spinning strategy may be attributed to whether there is an intermediate representation or not, which could explain why depth rotation is faster.

Adult↗

PubMed2002

Inhibitory tagging on randomly moving objects.

Inhibitory tagging is a process that prevents focal attention from revisiting previously checked items in inefficient searches, facilitating search performance. Recent studies suggested that inhibitory tagging is object rather than location based, but it was unclear whether inhibitory tagging operates on moving objects. The present study investigated the tagging effect on moving objects. Participants were asked to search for a moving target among randomly and independently moving distractors. After either efficient or inefficient search, participants performed a probe detection task that measured the inhibitory effect on search items. The inhibitory effect on distractors was observed only after inefficient searches. The present results support the concept of object-based inhibitory tagging.

Adult↗