Temporal Expectation Improves the Quality of Sensory Information

In their letter, Nieuwenhuis et al. suggest that temporal expectation may affect the onset, rather than the rate, of evidence accumulation. They correctly pointed out a discrepancy between our results and previous findings, in which temporal expectation benefits performance by reducing the time needed for stimulus encoding (Bausenhart et al., 2010; Jepma et al., 2011; Seibold et al., 2011). Their main argument is that the model used in our study (Palmer et al., 2005) is not appropriate for tasks in which the duration of evidence accumulation is limited by backward masking. Though we concede that it is important to find a reason for the divergence between findings, we disagree with their line of argumentation, mainly because we do not think that our stimuli were backward masked to any significant extent.

In our study, targets were presented for 50 ms and were followed by a standard (irrelevant) stimulus at a fixed interval of 400 ms (identical in regular and irregular conditions). During the inter-stimulus interval, a gray screen with a light-gray circle positioned around target area was presented, with no noise or masking of any kind. Thus, only the next stimulus could have masked the target. However, the long interval between stimuli precludes any significant effects of backward masking. In general, backward masking is known to be strongly SOA-dependent, peaking before 100 ms and decaying long before 400 ms (Breitmeyer and Ogmen, 2006). Similarly, modeling studies have also shown that masking should not disrupt the diffusion process after 200-300 ms following target onset (see Smith and Ratcliff, 2009 for a review). In particular, although one could argue that the subsequent stimulus could have disrupted the representation of the target in visual short-term memory (VSTM), previous findings suggest that the strength of the VSTM trace has reached its asymptote after 400 ms in conditions similar to ours (Smith and Ratcliff, 2009). Therefore, it is unlikely that the presentation of the standard stimulus has any influence on the dynamics of the ongoing diffusion process.

Nevertheless, we agree with Nieuwenhuis et al. that the discrepancy between our results and earlier findings calls for an explanation. We believe that a major contributing factor may be the methods used to induce temporal expectations. In our task, temporal expectation was generated by the regular isochronic rhythmic presentation of stimuli. In the previous experiments mentioned by Nieuwenhuis and colleagues, temporal expectation was induced by foreperiod effects or voluntary temporal attention (Jepma et al., 2011; Seibold et al., 2011). In Jepma et al., for example, temporal expectation was manipulated by having a fixed cue-target delay in a blocked design (experiment 1), or by using symbolic cues in a simple reaction-time task (experiment 2). The mechanisms supporting different types of temporal expectation may not always be the same. For example, dissociations have been noted in mechanisms supporting temporal expectations generated by rhythm versus symbolic cues (Coull and Nobre, 2008; Rohenkohl et al., 2011). Additionally, invasive studies have found that cortical oscillations in early sensory regions become entrained to external rhythms as a mechanism of selective attention. If these oscillations reflect structured fluctuations in cortical excitability, then it is plausible that they can lead to more efficient processing of sensory information occurring at expected moments. As ever, further experimentation using different methods for generating temporal expectations in diverse modalities and under text demands will be useful to conciliate or adjudicate between competing explanations.

References:

Bausenhart KM, Rolke B, Seibold VC, Ulrich R (2010) Temporal preparation influences the dynamics of information processing: evidence for early onset of information accumulation. Vision research 50:1025-1034.

Breitmeyer BG, Ogmen H (2006) Visual Masking: Time Slices Through Conscious And Unconscious Vision. Oxford University Press.

Coull J, Nobre A (2008) Dissociating explicit timing from temporal expectation with fMRI. Current opinion in neurobiology 18:137-144.

Jepma, M., Wagenmakers, E.-J., and Nieuwenhuis, S. (2012). Temporal expectation and information processing: A model-based analysis. Cognition, 122, 426-441.

Palmer J, Huk AC, Shadlen MN (2005) The effect of stimulus strength on the speed and accuracy of a perceptual decision. Journal of Vision 5:376-404.

Rohenkohl G, Coull JT, Nobre AC (2011) Behavioural dissociation between exogenous and endogenous temporal orienting of attention. PloS one 6:e14620.

Seibold, V. C., Bausenhart, K. M., Rolke, B., and Ulrich, R. (2011). Does temporal preparation increase the rate of sensory information accumulation? Acta Psychologica, 137, 56-64.

Smith PL, Ratcliff R (2009) An integrated theory of attention and decision making in visual signal detection. Psychological review 116:283- 317.

Conflict of Interest:

None declared