Page 22 - It' about time: Studying the Encoding of Duration

General introduction In this dissertation we employ the technique of sensory adaptation to answer several questions about duration-tuned mechanisms and the role 1 they play in duration encoding. The occurrence of the DAE reflects changes in activation in the neural structures responsible for duration encoding. As such, we can use the occurrence, or relative magnitude, of the DAE as a measurement of the activation occurring within duration-tuned neural structures during adaptation. By manipulating experimental condition during adaptation we can measure the effect of these manipulations on the duration encoding process. This allows us to probe the duration encoding process and draw conclusions about the underlying neural structures and their functional properties. In this way, the DAE provides a unique tool that allows us to study the spatial and temporal properties of duration encoding, as well as studying the extraction of duration information from different sources of sensory information under different behavioral circumstances. In chapter 2, we study the relative position of duration-tuned mechanisms along the visual processing hierarchy. The area of visual space over which sensory information is integrated increases along the visual processing hierarchy (A. T. Smith, Singh, Williams, & Greenlee, 2001). As a result, adaptation occurring early on in the visual processing hierarchy leads to after-effects that are restricted to relatively small areas of visual space surrounding the adapted location. In contrast, adaptation occurring at later stages of visual processing leads to after-effects that spread across increasingly larg areas of visual space around the adapted location. We measure the DAE at different adapter-test distances and found no evidence of spatial selectivity for the DAE. From this, we conclude that duration is a feature that is encoded relatively late in the visual processing hierarchy. The fact that the DAE shows no spatial selectivity also established important groundwork for the manipulations/paradigms used in future studies, allowing for spatial manipulations during adaptation which were used in chapter 3 and 4. In chapter 3, we investigate the role of attention in the selective encoding of duration when multiple sources of duration are present. At any given time, we are presented with a large amount of temporal information. This abundance of temporal information requires us to select relevant information to guide our behaviour, while avoiding the influence of irrelevant information. Attention has often been assumed to play an important role in gating duration information for subsequent encoding (Gibbon et al., 1984; Meck, 1984; 21