No abstract

We investigated how perceived duration of empty time intervals would be modulated by the length of sounds marking those intervals. Three sounds were successively presented in Experiment 1. Each sound was short (S) or long (L), and the temporal position of the middle sound's onset was varied. The lengthening of each sound resulted in delayed perception of the onset; thus, the middle sound's onset had to be presented earlier in the SLS than in the LSL sequence so that participants perceived the three sounds as presented at equal interonset intervals. In Experiment 2, a short sound and a long sound were alternated repeatedly, and the relative duration of the SL interval to the LS interval was varied. This repeated sequence was perceived as consisting of equal interonset intervals when the onsets of all sounds were aligned at physically equal intervals. If the same onset delay as in the preceding experiment had occurred, participants should have perceived equality between the interonset intervals in the repeated sequence when the SL interval was physically shortened relative to the LS interval. The effects of sound length seemed to be canceled out when the presentation of intervals was repeated. Finally, the perceived duration of the interonset intervals in the repeated sequence was not influenced by whether the participant's native language was French or Japanese, or by how the repeated sequence was perceptually segmented into rhythmic groups.

We quantitatively investigated the halt and recovery of illusory motion perception in static images. With steady fixation, participants viewed images causing four different motion illusions. The results showed that the time courses of the Fraser-Wilcox illusion and the modified Fraser-Wilcox illusion (i.e., "Rotating Snakes") were very similar, while the Ouchi and Enigma illusions showed quite a different trend. When participants viewed images causing the Fraser-Wilcox illusion and the modified Fraser-Wilcox illusion, they typically experienced disappearance of the illusory motion within several seconds. After a variable interstimulus interval (ISI), the images were presented again in the same retinal position. The magnitude of the illusory motion from the second image presentation increased as the ISI became longer. This suggests that the same adaptation process either directly causes or attenuates both the Fraser-Wilcox illusion and the modified FraserWilcox illusion.

'Rotating snakes' is an illusory figure in which the 'snakes' are perceived to rotate. We report that when the image moves smoothly, the snakes do not appear to rotate, although the retinal images are continuously refreshed. Therefore, to produce the illusion, the image should remain stationary (without being refreshed) for some time on the same retinal position.

Introduction Stratton (1896) was the first to investigate inverted vision by using a prism. Since his initial work, many researchers have investigated several behavioural aspects of the adaptation process (Harris 1965). When subjects first wear such prism goggles, they usually experience nausea due to the unstable visual field caused by their head movements. However, it has often been reported that subjects could eventually even ride a bicycle. In general, adapting to a new visuo-motor coordination with rearrangement of proprioceptive information requires more than a week of adaptation (eg Stratton 1897a, 1897b; Peterson and Peterson 1938; Kohler 1964; Sekiyama et al 2000). During this period, the visual system itself also seems to adapt to the new situation (Shimojo and Nakajima 1981; Ichikawa et al 2003). Sugita (1996) revealed the kinds of changes in the brain that underlie the adapted behaviours. He showed that after 1Ã Ä months of adaptation to left^right reversing spectacles, some cells in monkey V1 (primary visual cortex) began to respond to stimuli presented not only in the contralateral visual field but also in the ipsilateral field. Recently, the same physiological change was observed in the human adult brain within only 4 or 5 days of wearing left^right reversing goggles (Miyauchi et al 2004). A psychophysical investigation also provides behavioural evidence of the reorganisation in the brain noted above (Tanaka et al 2007). In that study, perceptual learning was transferred to a mirror-symmetrical region across the vertical meridian through adaptation to left^right reversed viewing. The`mirror-drawing' (or`mirror-tracing') experiment, which has been a popular experiment as a class activity in psychology courses (Starch 1910), also tests a kind of adaptation to transformed vision. In a typical mirror-drawing experiment, subjects trace a star-shaped course (Scheidemann 1950), drawing a line while viewing their hand only through a mirror placed in front of them. The experimenter measures the time period required to go around the course and counts the number of times the subject goes off course as errors. The period required to complete a course is known to exhibit a negatively accelerating learning curve as a function of the trial number. Typical examples of learning curves in a mirror-drawing experiment with regard to completion time and number of errors as a function of the trial number can be seen in Borresen and Klingsporn (1992).