视听时间再校准：适应空间与适应客体的联合及独立作用

Audiovisual Temporal Recalibration: The Combined and Separate Effect of Adapted Space and Object

同一事件的视听成分即使同时发生,由于两种信息的物理传播与神经传导速度的差异,大脑知觉到它们的时刻仍会存在一定的延迟。时间再校准指大脑可以最小化并适应这段时间延迟的现象。本研究采用"适应—测验"范式,在适应阶段连续给被试呈现视觉先于听觉或听觉先于视觉128ms的刺激对,在测验阶段以时序判断任务来测量被试此时主观同时点的变化。通过操纵适应及新异视听刺激对(即适应客体与新异客体)在测验阶段出现的空间位置,探索空间与客体因素对视听时间再校准的影响。结果发现,当适应客体出现于适应空间时,主观同时点显著偏向了时间延迟的方向;同样显著或边缘显著的主观同时点偏移还发生于适应客体出现于未适应空间时,以及新异客体出现于适应空间时。研究表明,视听时间再校准在不同空间中的表现取决于适应空间与适应客体的联合或独立作用。

Previous researches have revealed that temporal recalibration arises from perceptual change rather than cognitive shift. And such a PSS（the point of subjective simultaneity） shift might coincide with changes in perceptual latency of a certain modality. Given the rich and variable environments we live in, multisensory events might not always appear in the central field as considerable experiments have done. There is no doubt that they could simultaneously or successively appear in the lateral space. If the participants were repeatedly exposed to asynchrony audiovisual pairs presented in lateral space （left or right）, will the aftereffects only be expected in the adapted space？ A recent study has shown that temporal reealibration was spatial-specific （Hanson, Roach, Heron, ＆ McGraw, 2008）, but can certain audio-visual（abbreviated to AV） object play some roles in temporal recalibration？ Now we found a new way to test the combined effect of adapted space and object, and to separate the two individual effects. To the end, two experiments were designed. Each experiment was comprised of an exposed and a test phase. In the exposed phase of the first experiment, certain asynchrony audiovisual stimulus pairs were repeatedly displayed in the left or right space with a fixation in the screen center on which participants were required to freeze their eyes throughout the whole experiment. While in the test phase, we presented the adapted AV pairs in the adapted space but novel AV pairs in the opposite space. In the second experiment, the procedure was the same with the first one except that we put the adapted AV pairs in the opposite space and the novel ones in the adapted space. Through these two experiments, we first aim to replicate the spatial-specific findings when adapted AV pairs （object） recurred in the adapted space, then to explore whether the separate effect of adapted object and adapted space would induce temporal recalibration as well. In Experiment 1, after repeated exposure to 240 trials with constant temporal lag in a block, either with auditory stimulus leading 128ms or visual stimulus leading 128ms, the participants shifted their PSS towards the leading modality, only in the adapted space. In Experiment 2, if the temporal recalibration were restricted to the combined effect of adapted space and object, there would be no observed PSS shifts. But violating such inference, the participants still showed significant PSS shifts in the adapted AV pairs and approaching-significant PSS shifts in the adapted space, although the magnitude was no so great as in Experiment 1. Comparing the results of the two experiments, we concluded that when adapted object kept its position across the exposed and test phase, audiovisual temporal recalibration showed as specific, in other words, aftereffects only exists in the adapted space or adapted object; but when separating the effect of space and object, temporal recalibration was neither spatial- nor object-specific. That is to say if the adapted stimulus pairs changes its location after exposure, wherever it stops, aftereffects would be subsequently induced in that new space, while in the adapted space aftereffects stills remains although novel object replaced the adapted one. The outcome of temporal recalibration then ought to be characterized as the separate effect of adapted space and adapted object, or the combined effect of both.