Apparent causality affects perceived simultaneity.

The present research addresses the question of how visual predictive information and implied causality affect audio-visual synchrony perception. Previous research has shown a systematic shift in the likelihood of observers to accept audio-leading stimulus pairs as being apparently simultaneous in variants of audio-visual stimulus pairs that differ in (1) the amount of visual predictive information available and (2) the apparent causal relation between the auditory and visual components. An experiment was designed to separate the predictability and causality explanations, and the results indicated that shifts in subjective simultaneity were explained completely by changes in the implied causal relations in the stimuli and that predictability had no added value. Together with earlier findings, these results further indicate that the observed shifts in subjective simultaneity due to causal relations among auditory and visual events do not reflect a mere change in response strategy, but rather result from early multimodal integration processes in event perception.

Temporal order judgment criteria are affected by synchrony judgment sensitivity.

Synchrony perception for audio-visual stimulus pairs is typically studied by using temporal order judgment (TOJ) or synchrony judgment (SJ) tasks. Research has shown that estimates of the point of subjective simultaneity (PSS) obtained using these two methods do not necessarily correspond. Here, we investigate the hypothesis that the PSS estimate obtained in a TOJ task is shifted in the direction of the most sensitive part of the synchrony judgment curve, as obtained in an SJ task. The results confirm that criterion shifts in the TOJ task move the PSS toward regions of the audio-visual temporal interval continuum where discriminations are most sensitive.

Temporal interval discrimination thresholds depend on perceived synchrony for audio-visual stimulus pairs.

Audio-visual stimulus pairs presented at various relative delays, are commonly judged as being "synchronous" over a range of delays from about -50 ms (audio leading) to +150 ms (video leading). The center of this range is an estimate of the point of subjective simultaneity (PSS). The judgment boundaries, where "synchronous" judgments yield to a predominance of "asynchronous" judgments, usually include physical synchrony, or the point of objective simultaneity (POS). When the POS is used as a standard in a delay discrimination paradigm, thresholds tend to be asymmetric; that is, smaller on the audio-leading side than on the video-leading side of the standard. We replicated this finding using different stimulus types, and standards distributed within and beyond the synchrony judgment boundaries. Thresholds were symmetric near the center of the synchrony range (PSS), but showed opposite patterns of asymmetry as the standard approached either of the two synchrony judgment boundaries. That is, apparent synchrony shows a type of categorical perception in that discriminations within the synchrony category are difficult, but those near the category boundary are easy.

Audiovisual synchrony and temporal order judgments: effects of experimental method and stimulus type.

When an audio-visual event is perceived in the natural environment, a physical delay will always occur between the arrival of the leading visual component and that of the trailing auditory component. This natural timing relationship suggests that the point of subjective simultaneity (PSS) should occur at an auditory delay greater than or equal to 0 msec. A review of the literature suggests that PSS estimates derived from a temporal order judgment (TOJ) task differ from those derived from a synchrony judgment (SJ) task, with (unnatural) auditory-leading PSS values reported mainly for the TOJ task. We report data from two stimulus types that differed in terms of complexity--namely, (1) a flash and a click and (2) a bouncing ball and an impact sound. The same participants judged the temporal order and synchrony of both stimulus types, using three experimental methods: (1) a TOJ task with two response categories ("audio first" or "video first"), (2) an SJ task with two response categories ("synchronous" or "asynchronous"; SJ2), and (3) an SJ task with three response categories ("audio first," "synchronous," or "video first"; SJ3). Both stimulus types produced correlated PSS estimates with the SJ tasks, but the estimates from the TOJ procedure were uncorrelated with those obtained from the SJ tasks. These results suggest that the SJ task should be preferred over the TOJ task when the primary interest is i n perceived audio-visualsynchrony.

Storage of verbal associations is sufficient to activate the left medial temporal lobe.

Neuroimaging studies have shown that memory encoding activates the medial temporal lobe (MTL). Many believe that these activations are related to novelty but it remains unproven which is critical - novelty detection or the rich associative encoding it triggers. We examined MTL activation during verbal associative encoding using functional magnetic resonance imaging. First, associative encoding activated left posterior MTL more than single word encoding even though novelty detection was matched, indicating not only that associative encoding activates the MTL particularly strongly, but also that activation does not require novelty detection. Moreover, it remains to be convincingly shown that novelty detection alone does produce such activation. Second, repetitive associative encoding produced less MTL activation than initial associative encoding, indicating that priming of associative information reduces MTL activation. Third, re-encoding familiar associations in a well-established way had a minimal effect on both memory and MTL activation, indicating that MTL activation reflects storage of associations, not merely their initial representation.