Simultaneity and temporal order perception: Different sides of the same coin? Evidence from a visual prior-entry study

Abstract

Attended stimuli are perceived as occurring earlier than unattended stimuli. This phenomenon of prior entry is usually identified by a shift in the point of subjective simultaneity (PSS) in temporal order judgements (TOJs). According to its traditional psychophysical interpretation, the PSS coincides with the perception of simultaneity. This assumption is, however, questionable. Technically, the PSS represents the temporal interval between two stimuli at which the two alternative TOJs are equally likely. Thus it also seems possible that observers perceive not simultaneity, but uncertainty of temporal order. This possibility is supported by prior-entry studies, which find that perception of simultaneity is not very likely at the PSS. The present study tested the percept at the PSS in prior entry, using peripheral cues to orient attention. We found that manipulating attention caused varying temporal perceptions around the PSS. On some occasions observers perceived the two stimuli as simultaneous, but on others they were simply uncertain about the order in which they had been presented. This finding contradicts the implicit assumption of most models of temporal order perception, that perception of simultaneity inevitably results if temporal order cannot be discriminated.

Keywords:

• Prior entry
• Temporal order judgement
• Simultaneity
• Attention

The research reported in this paper was supported by the Deutsche Forschungsgemeinschaft (DFG), Grant Ne 366/7–2 to Ingrid Scharlau. We thank Ulrich Ansorge, Frederic Hilkenmeier, and two anonymous reviewers for helpful comments on earlier versions of the paper and Heinz-Werner Priess and Jan Tünnermann for programming parts of the software. Parts of the data in this manuscript were presented at the 50. Tagung experimentell arbeitender Psychologen [50th Conference of experimentally working psychologists], 30th March to 1st April, 2008, Marburg, Germany, and at the Herbsttagung Experimentelle Kognitionspsychologie [Autumn Conference on Experimental Cognitive Psychology], 31st October to 2nd November, 2008, Dresden, Germany.

Notes

¹ But note that some studies in both unimodal and cross-modal prior entry did not find a PSS exactly at an SOA of zero in the control conditions (e.g., Shore et al., 2001; Zampini et al., 2005b).

² Note that recent studies on prior entry by masked cues termed the speed-up as “perceptual latency priming”, relating it to the broader topic of processing of nonconscious information (priming). As this is of no special relevance for the present study, we use the more common term “prior entry” here.

³ We want to stress that DLs computed from binary and multiple-alternative TOJs cannot be compared directly, because the additional judgement alternatives reduce error variance for the two order judgements. In consequence, psychometric functions are probably steeper in TOJs with more than two alternatives. DLs should therefore be smaller.

⁴ Note that we can only derive rough assumptions about DL from the temporal-profile model. The reason is that the temporal-profile model makes assumptions about discrimination accuracy for each SOA separately whereas DL is a parameter which applies to the whole psychometric function.