Abstract: Previous researches have indicated that attention can modulate subjective time perception: the less the attention distributed to duration, the more the chances of time being misperceived. Most brain mechanism studies have focused on the comparison between temporal and nontemporal conditions. These studies were confined to the attention shift between temporal and nontemporal attributes, and did not refer to the process of attentional modulation of time perception. A recent research studied the cerebral areas concerned with the attentional modulation of time perception using functional magnetic resonance imaging (fMRI). The study employed a dual-task paradigm in which attention was distributed differently between the time and color of the visual stimulus. However, the dynamic process of attentional modulation of time perception was still unclear because of the low temporal resolution of the fMRI. In contrast, this experiment used event-related potentials (ERPs) to investigate this process.
Nineteen volunteers participated in this experiment. All subjects performed a training session at least two days before the formal experiment. An attentional cue directed the subjects to selectively attend to (1) the stimulus time (T condition), (2) the time rather than the pitch (Tp condition), (3) both parameters equally (tp condition), (4) the pitch rather than the time (tP condition), or (5) the pitch (P condition). Effective attentional allocation was obtained by varying the relative likelihood of trials involving time distinguishing or those involving pitch distinguishing. The reaction time, error rate, and event-related potentials were recorded simultaneously by computers during the experiment.
The electroencephalogram (EEG) was recorded from 64 scalp locations of the extended 10–20 system, using an electrode cap (Brain Product Inc.) with Ag/AgCl electrodes. Linked mastoids were used as the reference, and a ground electrode (GND) was placed on the medial aspect of the frontal lobes (on the middle line, between FZ and FCz). An estimation of the dipolar sources of the T-P difference waveform was performed using the Brain Electrical Source Analysis program (BESA version 5.0), which is based on the four-shell ellipsoidal head model. Further, a principal component analysis (PCA) was employed in the interval from 300 to 540 ms in order to estimate the minimum number of dipoles. Finally, a genetic algorithm was used to determine the location of the dipoles.
Behavioral data showed that the subjects allocated their attention to the time and pitch based on the attentional cues. The ERP data indicated the following: (1) the main effect of the attentional conditions in the amplitude of P2 was not significant, but the difference between the T and P conditions was significant in the multiple comparison; (2) the main effect of the attentional conditions in the average amplitude of the contingent negative variation (CNV) was significant from the start latency time to 540ms, and an increase in the attention to time augmented the average amplitude of the CNV; (3) the map of the T-P difference waveform showed that the maximal amplitude of the difference waveform was located on the areas of the frontal, center, and parietal lobes; and (4) the dipoles of the T-P difference waveform were located on the supplementary motor area (superior frontal gyrus, middle frontal gyrus) and the inferior parietal lobule.
These results have the following implications: (1) the time information process exists in P2 phase; (2) CNV reflects the attentional modulation of time perception, which is an index of the existing controlled process; (3) the supplementary motor area may play a key role in time perception with cross-modal effect; and (4) the inferior parietal lobule is also related to the attention of time, albeit time attention is not the only attribute. However, these results are contradictory to Lewis’ notion that (1) a “second” is the boundary between an “automatic” and a “cognitively controlled” timing system and (2) the supplementary motor area belongs only to the “automatic timing system.”

Key words: time perception, attention, contingent negative variation, supplementary motor area, inferior parietal lobule