Abstract
Intro: A salient event embedded in a stream of serially presented identical stimuli can be perceived as lasting longer than its veridical duration. This subjective expansion of time (SET) might be due to the sudden allocation of attentional resources to the salient event (Tse et al., 2004). Recent studies on patients with damage to the right Inferior Parietal Lobe (rILP) suggest that this area plays a crucial role in the attentional network that is involved in discriminating events across time. In the present study we stimulated the IPL to understand its causal relationship with the subjective experience of time. We used an offline repetitive transcranial magnetic stimulation (rTMS) paradigm and measured SET before and after stimulation. Method: 10 participants took part in a 2AFC oddball discrimination task, in which they had to choose whether an infrequent ‘oddball’ (20% chance of presentation) of varying durations (staircase procedure) lasted "longer" or "shorter" compared to a frequent ‘standard’ (80%) constant duration (1050msec) stimulus. Each participant attended three counterbalanced sessions, where 10 min 1 Hz rTMS was administered on three different sites: rIPL, left-IPL and Occipital as a control site. SET was measured three times during each session: baseline before rTMS, post-rTMS and 30 minutes delayed-rTMS. Results: Analysis revealed a main effect of stimulation site, with an increased effect of the ‘times expansion’ factor after rIPL stimulation. Only after rIPL stimulation the ‘oddball’ had to be presented for a shorter time in order to be perceived to last the same amount of time as the ‘standard’. TMS over left-IPL or Occipital had no effect. Conclusion: These data provide further evidence of the role of the rIPL in temporal processing of visual events. This function appears to depend on higher-order attentional mechanisms that are supported by the ‘When’ pathway of the right parietal lobe.
Meeting abstract presented at VSS 2013