Page 120 - It' about time: Studying the Encoding of Duration

to encode duration. First, I discussed the existence of tuned behavioral responses such as the DAE which occurs after sensory adaptation (Heron et al., 2012). I argued that the occurrence of tuned behavioral responses reflects the existence of duration-tuned neural structures. Secondly, I discussed evidence for the existence of duration-tuned neural responses in different areas of the brain, measured in both humans (Hayashi et al., 2015, 2018; Protopapa et al., 2018) and non-human animals (Duysens et al., 1996; Ehrlich et al., 1997; He & Hashikawa, 1998; Merchant, Pérez, et al., 2013; Mita et al., 2009). These results demonstrate that humans possess neural substrates that could underly the reported tuned behavioral response, providing a possible mechanism for duration encoding. Given the parallel between these two sets of results, it seems likely that tuned behavioral responses reflect a behavioral consequence of processes occurring in duration-tuned neural structures. However, there is no direct evidence linking tuned behavioral responses to the tuned responses observed in neurophysiological recordings and neuroimaging studies in humans. Without direct evidence linking the two, it is possible that the observed tuned behavioral responses occur independently of the reported tuned neural responses (Teller, 1984). To address this issue, future work should aim to measure the effects of adaptation on both neural responses and behavior concurrently. For example, by combining fMRI decoding of duration with adaptation paradigms it should be possible to demonstrate changes in neural responses following duration adaptation while also showing that these changes have predictive value for subsequent duration judgements. Alternatively, studies could aim to directly affect the responsiveness of duration sensitive neural structures (e.g. lesion studies in non-human animals, rTMS in human observers) and measure the consequences on timing behavior. By incorporating these techniques into the 6 study of duration perception it should be possible to provide stronger evidence for the assumed causal relation between duration-tuned neural responses and tuned behavioral responses. Unifying theories of duration perception The studies described in chapters 2,3 and 4 of this dissertation focussed strongly on the framework of channel-based duration encoding. This strong focus on a single framework raises the question as to why there is no discussion General discussion 119