The Role Of The Number Of Encoded Spatial Locations In Time Perception:Behavior And Erp Evidence

Time perception is a fundamental process in human cognition. In recent years, a large number of researches reveal that various physical properties (such as size, lightness, physical distance, speed, movement direction, visibility, etc.) can exert a direct influence on subjective time perception. However, up to now, there is no direct study to explore whether encoded spatial locations might have a role in subjective time estimation. The purpose of the present study was to see whether time perception could be influenced by different encoded spatial locations. In this study, we used a new paradigm which we recently developed and named as spatial splitting of a temporal interval (SSTI). The essence of this paradigm was to measure how perceived duration of a physically-fixed temporal interval (1100ms, standard interval) varied by its encoded spatial locations (1,2,3,4or6location(s), i.e.1L,2Ls,3Ls,4Ls and6Ls). In the four conditions of2Ls,3Ls,4Ls and6Ls, although multiple spatial locations were encoded, a single object and its occupied single spatial location were presented at any give moment to indicate the continuation of the standard interval, so did for the1L condition. This feature is a critical departure of our paradigm from previous others, such as Xuan, et. al.(2007), which demonstrated a perceived time expansion induced by simultaneously-presented multiple objects on the display.In this study, all of five experiments use a temporal comparison task. On each trial, one interval always contained a standard interval with the fixed standard duration (1100ms). In the other interval, a reference interval was presented with one of the seven or three comparison durations (from200ms to3000ms). The independent variable of all experiments are how many spatial location(s)(1L,2Ls,3Ls,4Ls and6Ls)were involved in the standard interval, and the dependent variable is time dilation coefficient(except for study3, in this experiment, the dependent variable are the frequency of’longer’ responses of the standard interval, reaction time and EEG indices). Experiment1showed that the main effect of encoded spatial locations is significant. Particularly, the perceived duration averaged across1L and2Ls conditions was significantly smaller than the perceived duration averaged across3Ls and4Ls conditions. Since the stimuli in Experiment1might suffer from the effect of different predictabilities for the different conditions, we performed Experiment2to rule out this account by using a fixed order of location sequence (clockwise or anticlockwise) in standard interval. Both experiments produced similar and largely consistent results. According to the results of Experiment1and Experiment2, we proposed that the temporal processing in visual modality might be constrained by spatial processing when time estimations were based on information of encoded spatial locations. That is the effect of number of encoded spatial locations on time perception-the more number of spatial locations we need to encode, the longer duration we perceive. After ruling out different predictabilities across the four standard conditions, the effect is also existence. And furthermore, we hypothesized that the location-number-related effect may reach a plateau at around three to four spatial locations. We performed Experiment3to verify this hypothesis. The result showed that the effect of encoded spatial locations is around the limit of three to four spatial locations (there is no difference in4Ls and6Ls conditions). We performed Experiment4to use a fixed order of location sequence in standard interval as a control experiment of Experiment3, the effect of encoded spatial locations was also present and its capacity was three to four spatial locations. All of our results suggest that the spatial constraint on temporal process is very likely around the limit of three to four spatial locations. In study3, we wanted to use ERP technology to seek for the electrophysiological indicator of the effect of encoded spatial locations. The results showed that the time processing based on spatial locations mainly reflected in the parietal-occipital area; the CNV peak was an index of time-based decision making; when the duration of the compared stimulus was1500ms, the CNV mean amplitude was more negative in1-2Ls conditions than in3-4Ls conditions in the time window that from1500ms to the subject’s decision (the peak latency).In short, through a series of experiments in this study, we proposed that the temporal processing in visual modality might be constrained by spatial processing when time estimations are based on information of encoded spatial locations, and the location-number-related effect might reach a plateau at around three to four spatial locations.