Keywords: time perception; illusion; empty interval; filled intervals; cluster analysis

Transcription

1 Journal of Sound and Vibration Manuscript Draft Manuscript Number: JSV-D Title: Does filled duration illusion occur for very short time intervals? Article Type: Rapid Communication Keywords: time perception; illusion; empty interval; filled intervals; cluster analysis Abstract: Subjective durations of filled time intervals (marked by the onset and offset of a sound) and empty time intervals (marked by onsets of two successive brief sounds) of ms were measured, utilizing the method of adjustment. Whereas many previous studies employing longer intervals had reported that filled time intervals had been perceived as longer than empty time intervals of the same physical duration (filled-duration illusion), the present results showed that this illusion occurred only for less than a half of the participants, and that, for the other participants, filled time intervals were perceived as shorter than empty time intervals.

2 Manuscript Click here to download Manuscript: HasuoNakajimaUeda_r2.doc Click here to view linked References Does filled duration illusion occur for very short time intervals? Emi Hasuo Graduate School of Design, Kyushu University Shiobaru, Minami-ku, Fukuoka, , Japan Yoshitaka Nakajima and Kazuo Ueda Department of Human Science, Kyushu University Shiobaru, Minami-ku, Fukuoka, , Japan Corresponding author: Emi Hasuo Graduate School of Design, Kyushu University Shiobaru, Minami-ku, Fukuoka, , Japan phone:

3 Abstract Subjective durations of filled time intervals (marked by the onset and offset of a sound) and empty time intervals (marked by onsets of two successive brief sounds) of ms were measured, utilizing the method of adjustment. Whereas many previous studies employing longer intervals had reported that filled time intervals had been perceived as longer than empty time intervals of the same physical duration (filled-duration illusion), the present results showed that this illusion occurred only for less than a half of the participants, and that, for the other participants, filled time intervals were perceived as shorter than empty time intervals. Keywords: time perception, illusion, empty interval, filled interval, cluster analysis Nomenclature: 130 M Human responses to sound and vibration: laboratory studies, field trials, exposure metrics, dose-response relationships; human structure interaction; hearing protection; vibration protection 2

4 1. Introduction The present article examines the filled duration illusion with very short time intervals. The filled duration illusion refers to the phenomenon that a filled interval is perceived to be longer than an empty interval of the same physical duration, and it has been demonstrated repeatedly in many psychophysical studies (e.g., Craig [1]; Zwicker, [2]; Wearden et al. [3]). We refer to a filled interval as the duration between the onset and the offset of a continuous sound, and an empty interval as the duration between two very brief sounds (e.g., Grondin [4]). Wearden et al. [3], who utilized such stimuli, found that the amount of the filled duration illusion increased as the stimulus duration lengthened, for intervals ranging from 77 to 1183 ms. The authors explained the results by suggesting that the pacemaker in the clock-switch-accumulator model runs faster during a filled interval. Wearden et al. s [3] study is highly important for its implication on the mechanism underlying the perception of filled and empty time intervals. Examining their results closely, we noticed three interesting points: First, for stimulus durations shorter than approximately 300 ms, the amount of the filled duration illusion seemed very small and even almost vanished in the shortest interval of 77 ms. Second, if the relationship between the stimulus 3

5 duration and the subjective duration held, the subjective duration for a 0-ms stimulus should be a positive value, not zero, according to their data. This is qualitatively consistent with the processing time hypothesis proposed by Nakajima [5], which assumes that the subjective duration of a short time interval is proportional to its physical duration plus a positive constant of about 80 ms. Third, the standard deviation of the responses for filled intervals in their data were constantly larger than those for empty intervals when the stimulus duration was shorter than 500 ms. It seemed possible that short time intervals below 500 ms are perceived in a different way from the way longer intervals are perceived, and additional theories to the pacemaker-speed hypothesis may be useful for very short time intervals. This is in line with some theories (e.g. Rammsayer [6]) suggesting different timing mechanisms for shorter (<~ 0.5 s) and longer (> 1 s) time intervals. There had not been many studies on filled duration illusion with such short intervals. Zwicker [2] utilized intervals as short as 5 ms, and the results did not seem to show clear filled duration illusion for intervals below 100 ms. As a first step, we focused on time intervals shorter than 200 ms, and examined the occurrence of the filled duration illusion. Perception of short time intervals within this range can be closely related to speech and music perception (e.g., Patel [7]; Fraisse [8]). 4

6 2. Method 2.1. Participants. Twenty-four undergraduate students of Department of Acoustic Design, Kyushu University, participated for course credits. All of them had received training in technical listening for acoustic engineers (Iwamiya et al. [9]). This training focused mainly on developing the ability to discriminate timbres and levels of sounds, and did not include training related to time perception Stimuli and apparatus. Each presentation consisted of a standard and a comparison in this order. The standard began s after the participant clicked the play button on the computer screen, and the comparison began s after the standard ended. The duration of these silences was randomized in a range of 500 ms for each presentation in order to prevent the participants from anticipating the beginnings of each stimulus too accurately. The standard duration was marked by either the onsets of two 20-ms sounds (empty-interval condition), a continuous sound (filled-interval condition), or the onsets of two 2-ms sounds (control condition). The comparison duration was always marked by two 2-ms sounds (an empty time interval as in the control condition). Sound duration included a rise and a fall time, which were 1 ms for the 2-ms sounds, and 10 ms for the other sounds of 20 to 180 ms. The envelope of the rise and fall portions was cosine-shaped in the intensity 5

7 dimension (Figure 1). All stimulus sounds were 1000-Hz pure tone bursts, and the total energy of each sound was kept constant. The presentation level of the 20-ms sound was 71 dba, measured as the level of a continuous tone of the same amplitude. The levels of the sounds were measured with a sound level meter (Node, 2072 or 2075) and an artificial ear (Brüel & Kjær, 4153). The standard duration was 20, 60, 100, or 180 ms (Figure 1). Thus, there were 12 experimental conditions (3 [filled, empty, and control] 4 [standard durations]). As empty intervals, we utilized onset-onset intervals. This was different from Wearden et al. [3] who defined their unfilled (click) intervals as offset-onset intervals. However, utilizing onset-onset intervals was important for us, because human auditory system is more sensitive to sound onsets than to offsets (e.g., Fastl & Zwicker [10]), and high sensitivity was necessary to investigate the perception of very short intervals as in our case. Another point was that, we were interested in relating the results to rhythm perception as in speech and music, which had been known to be based on onset-onset intervals (e.g., Handel [11]). The stimulus patterns were generated digitally (16 bits; a sampling frequency of 44,100 Hz) on a computer (Asus, EeePC 4G), and presented diotically via a digital-to-analog converter (Onkyo, Wavio SE-U55GX), an active low-pass filter (NF, 6

8 DV8FL, 8300 Hz), an amplifier (Sansui, AU-α607XR), and headphones (Sennheiser, HDA200) to the participant. The stimulus patterns were presented to the participant in a soundproof room Procedure. Participants adjusted the comparison interval to make it subjectively equal to the standard interval. Printed instruction with words and illustrations was shown and read to each participant, and it was clarified that the empty interval was from the onset of a sound to the onset of a subsequent sound, and that the filled interval was from the onset to the offset of one continuous sound. The final duration of the comparison interval in each trial was recorded as the point of subjective equality, PSE. The lower limit for the comparison interval was set to be 5 ms, for shorter intervals may cause the two sounds marking the comparison interval to be perceived as one sound rather than two distinct sounds (Plack [12]). When the participant tried to adjust the comparison interval to be shorter than 5 ms, this intention was recorded, but the comparison interval in the next presentation was 5 ms. For each standard interval, there were an ascending series and a descending series, and the PSEs from these series were averaged for each participant. Thus, the total number of trials was 24 (12 [experimental conditions] 2 [ascending and descending]). 7

9 3. Results and discussion Figure 2a shows the mean PSEs plotted as a function of the standard duration and the interval types (empty, filled, and control). The PSEs of the empty, the filled, and the control condition were very close to each other. The filled duration illusion did not appear in this graph; the mean PSEs of the filled interval condition were not larger than those in the empty or the control condition. This was unexpected, given that the overestimation of a filled interval had been reported repeatedly. Although we did not find much difference between interval types in the mean PSEs, the standard deviations between participants seemed to be larger in the filled interval condition than in the other conditions; within ms for the empty interval condition, ms for the control condition, and ms for the filled interval condition (always the lowest values are for the 20-ms standards, and the highest are for the 180-ms standards). This led us to wonder whether the large variability in the filled interval condition was due only to task difficulty or to different listening strategies employed by each participant. Thus, we calculated the amount of overestimation of the filled interval [(filled PSE) (control PSE)], and of the empty interval [(empty PSE) (control PSE)], for each 8

10 participant, and submitted their normalized values to a hierarchical cluster analysis. Clusters were determined by the Ward method, which analyzed the squared Euclidean distance between points. For the filled interval condition (Figure 3a), participants were divided clearly into two groups, with 16 participants in one cluster (Cluster 1) and 8 participants in the other (Cluster 2). No such clear clusters appeared for the empty interval condition (Figure 3b). We calculated the mean PSEs for Clusters 1 and 2 separately, and plotted them against standard duration (Figure 2b, c). The graphs showed clearly that participants in Cluster 1 underestimated the filled intervals, whereas participants in Cluster 2 overestimated. This tendency was consistent throughout all standard durations, and indicated that the large variability for the filled time intervals was due to different listening strategies rather than to task difficulty only. The main effect of the cluster difference was significant in the results of a two-way (cluster standard duration) ANOVA, performed utilizing the PSEs of the filled interval condition, [F (1, 22) = , p <.001] (It was natural and trivial that PSEs changed as the standard duration changed). We also performed a two-way (interval type standard duration) ANOVA for each cluster. For Cluster 1, the main effect of the interval type was 9

11 significant, [F (2, 30) = , p <.001]. Dunnett s post hoc test was performed to compare the control condition with the empty and the filled interval condition, and revealed significant difference between the filled and the control condition (p <.001). The difference between the empty and the control was not significant (p >.05). For Cluster 2, the main effect of the interval type was also significant, [F (2, 14) = 9.510, p <.05], and Dunnett s post hoc test revealed significant difference between the filled and the control condition (p <.001), but not between the empty and the control condition (p >.05). The interaction between the interval type and the standard duration in the two-way ANOVA was not significant (p >.05) in both clusters. Summarizing, the filled interval condition was significantly different from the control, but the empty interval condition was not, in both clusters. The differences, however, were in different directions. For very short time intervals of ms, some participants overestimated filled intervals, as had been reported in previous studies (e.g., Wearden et al, [3]; Zwicker, [2]), whereas the other participants underestimated them. This was the first time such systematic underestimation of filled intervals was observed, and the occurrence of two different types of perception (overestimation vs. underestimation of filled intervals) could not be predicted from any of the previous studies. Although our results were 10

12 unexpected, they were still consistent with Wearden et al. [3] in one way; for time intervals below 500 ms, the standard deviations for the filled intervals were larger than those for empty intervals in Wearden et al. s [3] results. Some participants may have overestimated, and others may have underestimated the short filled intervals, also in their case. One noticeable point about our results was that even in the Cluster-1 participants, the amount of underestimation of the filled interval decreased, i.e., the mean PSE of the filled interval condition approached those of the empty and the control condition, at the longest standard duration of 180 ms. This could mean that the underestimation appears clearly only for very short time intervals as in the present experiment, and it should be interesting to test whether the underestimation for these participants would disappear for longer time intervals. 4. Conclusions We found that the well-established filled duration illusion (i.e., the phenomenon that a time interval filled with, for instance, a tone tends to appear longer than an empty interval of the same duration bordered by click sounds), does not occur for very short intervals (< 200 ms). Twenty-four participants were clearly divided into two groups; usual overestimation of the filled intervals occurred in one group, but in the other group with the majority of participants, a paradoxical underestimation occurred stably. The present results 11

13 should be important showing a possibility that human listeners perceive very short time intervals differently from longer ones. Acknowledgments The authors thank Simon Grondin and Hiroshige Takeichi for their valuable comments. This research was supported by grants to YN and KU from the Japan Society for the Promotion of Science ( , , and ). References [1] J. C. Craig, A constant error in the perception of brief temporal intervals. Perception & Psychophysics 13 (1973) [2] E. Zwicker, Subjektive und objective Dauer von Schallimpulsen und Schallpausen [Subjective and objective duration of sound impulses and sound pauses]. Acustica 22 (1969/70) [3] J. H. Wearden, R. Norton, S. Martin, O. Montford-Bebb, Internal clock processes and the filled-duration illusion. Journal of Experimental psychology: Human Perception and Performance 33 (2007)

14 [4] S. Grondin, Methods for studying psychophysical time, in: S. Grondin (Ed.), Psychology of Time, Emerald, Bingley, 2008, pp [5] Y. Nakajima, A model of empty duration perception. Perception 16 (1987) [6] T. H. Rammsayer, Neuropharmacological evidence for different timing mechanisms in humans. Quarterly Journal of Experimental Psychology 52B (1999) [7] A. D. Patel, Music, Language, and the Brain, Oxford University Press, New York, [8] P. Fraisse, Rhythm and Tempo, in: D. Deutsch (Ed.), The Psychology of Music, Academic Press, New York, 1982, pp [9] S. Iwamiya, Y. Nakajima, K. Ueda, K. Kawahara, M. Takada, Technical listening training: Improvement of sound sensitivity for acoustic engineers and sound designers. Acoustics, Science and Technology 24 (2003) [10] H. Fastl, E. Zwicker, Psychoacoustics: Facts and models, Springer-Verlag, Berlin, [11] S. Handel, The effect of tempo and tone duration on rhythm discrimination. Perception & Psychophysics 54 (1993) [12] C. J. Plack, The Sense of Hearing, Erlbaum, New Jersey,

15 Figure Captions Figure 1. The illustration of stimuli in the empty (a), filled (b), and control condition (c). The stimuli of the comparison were the same as those in the control condition. The temporal midpoints (or the beginnings depending on how we describe the patterns) of the rise/fall time were considered as the beginning and the end of a time interval. Time intervals of the standard were 20, 60, 100, and 180 ms. Figure 2. Mean points of subjective equality (PSEs) plotted as functions of the standard duration and the interval types. Open squares show the PSEs of the empty interval condition, closed circles those of the filled interval condition, and gray downward triangles those of the control condition. Error bars represent the standard deviations between participants. (a) all participants (n = 24), (b) Cluster 1 (n = 16), and (c) Cluster 2 (n = 8). Participants in Cluster 1 underestimated the filled intervals, whereas participants in Cluster 2 overestimated. Figure 3. Dendrograms of 24 participants established by hierarchical cluster analysis. (a) filled interval condition and (b) empty interval condition. 14

16 Figure(s) Figure 1 a b c 20 ms 10 ms 10 ms 10 ms 10 ms 2 ms 1 ms 1 ms Intensity Intensity Intensity Time Time Time interval Time interval Time interval Time

17 Figure(s) Figure 2 a 300 b 300 c PSE (ms) PSE (ms) PSE (ms) Standard duration (ms) Standard duration (ms) Standard duration (ms) Empty Filled Control

18 Figure(s) Figure 3 a b Rescaled Distance Cluster Combine Participant number Participant number Rescaled Distance Cluster Combine