Spatial effects on temporal categorisation

The perceived duration of intervals, as determined by the point of subjective equality, was affected by the height and depth of the signals experiment 1.. The duration of an interval loc

1 Introduction

The relationship between time and space has intrigued experimental psychologists interested in perceptual processes (eg Cohen et al 1954, 1955; Collyer 1977; Miyatani

1984 ^ 1985; Suto 1952, 1955; Yoblick and Salvendy 1970) almost as much as it has phys-icists interested in general relativity (Yourgrau 2005) The visual-perception literature is replete with space ^ time investigations, embodied in various more contemporary issues, including time-to-arrival or time-to-collision (see for instance Bootsma and Oudejans 1993) The literature on auditory perception has also shown the importance that spatial intervals between sound sources play in the temporal organisation of auditory sequences (Grondin and Plourde 2007; Lakatos 1993; ten Hoopen 1995)

Classical examples of the mutual influence between space and time are the comple-mentary kappa and tau effects (Jones and Huang 1982) The kappa effect refers to the subjective dilation of time when its interval is marked by more spatially distant events (Cohen et al 1953; Newman and Lee 1972; Price-Williams 1954) The tau effect refers

to the subjective dilation of space when its extent is marked by more temporally distant events (Helson 1930; Helson and King 1931)

These Greek effects are not always found The kappa effect typically occurs when three brief successive signalsö 1, 2, and 3ö are presented, marking intervals usually shorter than 1 s If intervals 1 ^ 2 and 2 ^ 3 are equal in time, the 1 ^ 2 duration is perceived as longer if the spatial distance between 1 and 2 is greater than the one between 2 and 3 Here, a response relative to the length of a single temporal interval

is made after each presentation of a sequence of only two visual signals, a constella-tion of spatial condiconstella-tions of the type that often does not reveal kappa effects With such a single-stimulus method (eg Morgan et al 2000), it has been shown that more spatial distance between the locations of sources of the signal marking time does not

Spatial effects on temporal categorisation

Marie-Eéve Roussel, Simon Grondinô

Eècole de Psychologie, Universite¨ Laval, Que¨bec, QC G1K 7P4, Canada;

e-mail: simon.grondin@psy.ulaval.ca

Peter Killeen

Arizona State University, Tempe, AZ 85287, USA

Received 20 November 2007; in revised form 25 September 2008

Abstract We examined the influence of spatial factors in temporal processing Participants categorised as short or long empty intervals marked by two brief flashes delivered from locations differing in height and depth (experiment 1), or from two of three locations on a vertical plane (experiment 2) The perceived duration of intervals, as determined by the point of subjective equality, was affected by the height and depth of the signals (experiment 1) Experiment 2 showed that the point of fixation plays a critical role in perceived duration The duration of an interval located in the upper visual field is perceived as longer when participants fixate the higher visual source and shorter when the fixation point is set in the middle; this latter result also generally applies when the fixation point is in the lower source Finally, for the sensitivity level, there was

a significant segment (upper versus lower)6direction (descending versus ascending) interaction in experiment 1; a similar interaction effect varied according to the fixation point in experiment 2.

In experiment 2, the Weber fractions were around 0.22 Most results can be explained in terms

of the need to shift attention from one visual sourceöfor marking time intervalsö to another.

ô Author to whom all correspondence should be addressed.

necessarily result in longer perceived duration Indeed, some studies have shown that more distance resulted in shorter perceived duration, both for visual signals (Guay and Grondin 2001) and auditory signals (Roy and Grondin 2005)

The purpose of the present study was to further test the effect of visual signals at different locations in space on the perceived duration of temporal intervals in condi-tions that might carry the single stimulus paradigm a step closer to the type that generate a kappa effect In the first experiment, the distance between the LEDs takes several values and the segments between two flashes are located at different combina-tions of depth and height (see figure 1) In the second experiment, the spatial distance between signals is kept constant, there is no manipulation of depth, and the segments have one of two heights; however, there is a control on the fixation point

The experiments also provide an opportunity to estimate the sensitivity for discrim-inating intervals in different visuospatial conditions, which includes an investigation conducted with two base durations, in experiment 2, in order to examine the change

of the variability over time

2 Experiment 1

Given the kappa effect, more space between visual signals should result in longer perceived duration Therefore, any condition providing an impression that there is more distance, or more space, between signals, might result in longer perceived duration In the present experiment, visual signals are delivered from several locations varying

in depth and in height in the visual field The stimuli consist of a high distant LED (A, for above, or away); a low, close LED (B, for below); an LED placed between A and B (M, for middle or matrix) In all experimental sessions, the interval in a given trial is marked by either A and M, or by M and B The M stimulus is set at one

of 25 locations (one location per session, 25 sessions) made of the combinations of

5 locations in depth, and 5 in height Within each session, the participant is presented with one of four intervals marked by the following combinations of LEDs: B ^ M,

M ^ A, M ^ B, and A ^ M Therefore, there are two intervals located in the upper visual field (M ^ A and A ^ M) and two in the lower visual field (B ^ M and M ^ B) Two of four signal sequences go in an ascending and receding direction (B ^ M and M ^ A), and two in a descending and approaching direction (A ^ M and M ^ B)

2.1 Method

2.1.1 Participants Ten Laval University students, aged 19 to 34 years (Mˆ 24 years) took part in the experiment They received Can $100 for their participation

2.1.2 Apparatus and stimuli The intervals to be discriminated were marked by 20 ms visual signals (markers) produced by two of three circular, red-light-emitting diodes (LEDs: Radio-Shack #276-088) During the entire experiment, the A and B LEDs remained at the same places: A was 400 cm away from participants and 210 cm above the floor, and B was 150 cm away and 10 cm above the floor The M LED took one of

25 locations (one per session), selected from 5 depth (M , M , M , M , and M )

A

M

B

A

M

B

Figure 1 Schematic of experiments 1 and 2.

by 5 height (Mh1, Mh2, Mh3, Mh4, and Mh5) possibilities (see figure 1 and table 1) The locations divided the distance in depth, or the distance in height, according to the following proportions: 0:25ÿ 0:75; 0:62 ÿ 0:38; 0:5 ÿ 0:5; 0:38 ÿ 0:62; and 0:75 ÿ 0:25 All aspects of the experiment were controlled by a Zenith microcomputer

2.1.3 Procedure Each trial consisted of the presentation of a single interval (the single-stimulus methodöMorgan et al 2000) There were 25 sessions, one for each of the 25 M locations One session began with 8 presentations of the standard interval, 335 ms, followed

by five blocks of 96 experimental trials Within each block, there were 24 presenta-tions, in a random order, of each of four marker condipresenta-tions, B ^ M, M ^ B, A ^ M, or

M ^ A For each of these four conditions, there were 3 repetitions, in a random order,

of each of the eight intervals The intervals lasted for 160, 210, 260, and 310 ms (short), and 360, 410, 460, and 510 ms (long), with arithmetic mean 335 ms

Each observer was seated in a chair, in a dimly lit corridor, and asked to indicate whether the interval presented belonged to the short or to the long category by press-ing the left or the right button, respectively The response box was on a table in front

of the participant One participant was assigned to each of the five following session orders (see table 1 for description of these conditions): conditions 1 to 25; conditions

6 to 25 followed by 1 to 5; conditions 11 to 25 followed by 1 to 10; conditions 16 to

25 followed by 1 to 15; and conditions 21 to 25 followed by 1 to 20 One participant was assigned to each of the five reversed session orders: conditions 25 to 1, etc

2.1.4 Data analysis For each participant and for each of the 100 conditions (2626565), 8-point psychometric functions were constructed, with the eight intervals on the x-axis and the probability of responding ``long'' on the y-axis Each point on the psychometric function was based on 15 presentations A pseudo-logistic function rule (Killeen et al 1997) was fit to the functions The pseudo-discrimination function is a psychometric function constructed on the assumption that Weber's law holds: that is, that the uncer-tainty associated with both training and test stimuli is proportional to their magnitude

It is called `pseudo' because it is not a true distribution function as it asymptotes below 1.0 In the case of the logistic function, the corresponding pseudo ^ logistic function is

pt ˆ f1 ‡ exp‰ÿ…t ÿ m†=wtŠgÿ1,

where m is the mean, or point of subjective equality (PSE) and w is the Weber fraction (WF)

Two indices of performance were estimated from each psychometric function: one reflecting the mean perceived duration and the other the sensitivity The key dependent variable was the PSE, the t value corresponding to the 0.50 probability of a long response

Table 1 Location of below (B), middle (M), and above (A) LED on height and depth plane.

0 150 212.5 245.5 275 304.5 337.5 400 in height

0

in depth

The shift of the PSE observed for different conditions can be interpreted as an indication

of differences in the perceived duration of the stimuli A shift of the PSE to the left indicates that the stimuli are more often reported to be long The standard deviation (SDˆ wm) of the psychometric functions around the PSE provided an index of sensitivity (Grondin 2001a, 2005; Grondin et al 2005; Killeen and Weiss 1987)

2.2 Results

For the 1000 psychometric functions (100 functions for each of the participants), the mean goodness-of-fit (R2

) is 0.94; with the exclusion of a few outliers (like one R2

value at 0.09), it increases to 0.98 Out of 1000 scores, there were 12 outlier values for the PSE, and 52 for the sensitivity (SD) An outlier for one given participant is a value that is more than two SDs for the distribution of scores for this person The replac-ing score is the mean of two scores based on two linear regression analyses, one for valid scores of all other participants, and one for valid score of a specific participant 2.2.1 Perceived duration The mean results for perceived duration in each condition are reported in table 2 Overall, the PSEs are larger than 335 ms, the base duration This indicates that participants tend to respond ``short'' more often than ``long''

A repeated-measures ANOVA, according to a 2 segments (upper/lower)62 series (ascending/descending)65 depth65 height design, was conducted on the PSEs The Greenhouse ^ Geisser correction was applied to degrees of freedom when required Only one main effect, depth, is significant (F4 36 ˆ 2:65, p 5 0:05, Z2ˆ 0:23) The PSE

is farther to the rightö indicating that durations are perceived as shorter ö when the

M LED is located at 245.5 cm from the participant (ie 86.4 cm beyond Bö table 2) The series6height interaction was significant (F4 36 ˆ 5:00, p 5 0:01, Z2

ˆ 0:36ö see figure 2) Five t tests for paired samples, with a level at 0.05/5 according to Bonferroni correction, were used to compare the ascending versus descending conditions for each

of the height conditions, but no difference was significant In addition, two repeated-measures ANOVAs were conducted for each series for comparing the different height conditions The analyses revealed no significant difference in the ascending series, but for the descending series, the effect was significant (F4 396ˆ 4:78, p 5 0:01, Z2

ˆ 0:05) with a significant linear trend (F1 99 ˆ 8:39, p 5 0:01, Z2

ˆ 0:08); higher signals resulted

in lower PSE

,

,

, ,

Table 2 Mean point of subjective equality (PSE, in ms) as a function of the height and depth

of the signals.

62.5 95.5 125 154.5 187.5 62.5 95.5 125 154.5 187.5 Ascending series Ðinferior segment Ascending seriesÐsuperior segment

Descending series Ðinferior segment Descending seriesÐsuperior segment

The segment6height interaction was also significant (F4 36 ˆ 4:35, p 5 0:01, Z2

ˆ 0:33ösee figure 3) Five t tests for paired samples were used to compare the upper versus lower conditions for each of the height conditions Significant differences were observed at the two highest locations of M (Mh4, t9 ˆ 3:80, p 5 0:01; and Mh5,

t9 ˆ 3:60, p 5 0:01) In both cases, the PSE is smaller when the interval is presented

in the lower portion In addition, two repeated-measures ANOVAs were conducted for each segment for comparing the different height conditions The analyses revealed no significant difference in the upper segment condition, but for the lower segment there were significant differences, but the series of t tests (with adjusted a) revealed no sig-nificant difference No other interactions were sigsig-nificant

2.2.2 Sensitivity The mean results for sensitivity in each condition are reported in table 3 Overall, the SDs vary between 60 and 108 ms A repeated-measures ANOVA, according

to a 2626565 design, was conducted on the SD Once again, the Greenhouse ^ Geisser correction was applied to degrees of freedom when required

No main effect was significant, and only two interaction effects were significant One is the series6segment interaction (F1 9 ˆ 6:09, p 5 0:05, Z2

ˆ 0:41) In the ascending condition, the SD in the upper segment condition is larger than the SD in the lower segment condition (t24 ˆ 2:99, p 5 0:05); and, on contrary, for the descending condition, the SD in the lower segment condition is larger than the SD in the upper segment condition (t24 ˆ 4:77, p 5 0:05)

The other significant effect is the series6height interaction (F4 36 ˆ 3:98, p 5 0:01,

2

ˆ 0:31) A comparison of the descending and ascending series for each height

,

,

,

370

365

360

355

350

345

340

335

330

Ascending series Descending series

Height of M=cm

Figure 2 Mean point of subjective equality ( SE) for each series as a function of the location of the middle (M) LED in exper-iment 1 Dots indicate base duration.

370

365

360

355

350

345

340

335

330

Lower segment Upper segment

Height of M=cm

Figure 3 Mean point of subjective equality ( SE) for each segment as a function of the location of the middle (M) LED in exper-iment 1 Dots indicate base duration.

condition revealed no significant difference (once the Bonferroni correction is applied, 0.05/5), but note that the SD was much smaller in the descending than in the ascend-ing condition at mid-height (110 cm; Mh3: t9 ˆ 2:79, p ˆ 0:021)

3 Experiment 2

In experiment 1, the height of the M signal exerted an effect on perceived duration, but this effect interacted with the fact that the intervals were presented in the upper or lower part of the visual field (VF), and with the fact that the sequence of signals was ascending (and going farther away) or descending (and getting closer to the partici-pant) For the intervals delivered in the lower part of the VF, the higher the M signal was, the longer was the perceived duration In other words, more space resulted in longer duration; however, this effect was restricted to the lower part of the VF In the upper part of the VF, a higher M signal meant a smaller distance between M and A, but this didn't lead to systematic effect on perceived duration Indeed, the impression that objects higher in the VF are located farther away applies to objects located below the fixation point on the horizon In other words, different results obtained for the lower versus upper parts of the VF might depend on the fixation point

The main purpose of experiment 2 is to provide a direct test of the influence on perceived duration exerted by the height in the VF of signals delimiting a temporal interval As indicated earlier, the height of objects in the VF contributes to the per-ception of distance, but this contribution might well depend on the point of fixation

in the horizon In this experiment, there is a series of comparisons of the effect on perceived duration of the interval location The distance between the signals marking the upper or lower intervals is kept constant (M remains equidistant between A and B) More specifically, the upper segment condition is either A ^ M or M ^ A, and the lower one is either M ^ B or B ^ M, and M has only one location (instead of 25 ö 565 ö as

in experiment 1) Staring at the A, M, or B point is probably a critical factor, not only because of the consequence on the interpretation of distance, but also because

a visual target is often detected more correctly and more rapidly when presented in the upper VF (Previc and Naegele 2001) and because the fixation point determines the distance between where attention is located and where it should be located (arrival point of the first marker) Finally, because there were fewer location points tested in the present experiment, the present investigation was extended to an additional range

of duration

Table 3 Mean standard deviation (SD, in ms) as a function of the height and depth of the signals

62.5 95.5 125 154.5 187.5 62.5 95.5 125 154.5 187.5 Ascending series Ðinferior segment Ascending seriesÐsuperior segment

Descending series Ðinferior segment Descending seriesÐsuperior segment

3.1 Method

3.1.1 Participants Thirteen Laval University students, nine females and four males, aged 21 to 30 years (Mˆ 25 years) took part in the experiment They received Can $60 for their participation

3.1.2 Apparatus and stimuli The material was the same as in experiment 1, but the experiment was conducted in another room, also dimly lit The intervals were marked

by two of three LEDs located 2 m in front of the participant on a vertical plane The LEDs were placed 50 cm apart, the middle (M) one being approximately at the height

of the participants' eyes (at 110 cm above the ground) Each LED subtended a visual angle of about 0.29 deg, with the visual angles between the middle LED and the one above (A) and the one below (B) both being 148

3.1.3 Procedure As in experiment 1, the single-stimulus method was used There were two base durations: 200 and 335 ms For the 200 ms base duration, intervals lasted

95, 125, 155, and 185 ms (short category), and 215, 245, 275, and 305 ms (long category), with arithmetic mean 200 ms In the 335 ms base duration condition, the intervals lasted 160 to 510 ms (same as in experiment 1) The interval was presented either in the lower part (B ^ M or M ^ B sequences) of the VF, or in the higher part (M ^ A

or A ^ M sequences) The direction of the sequence was referred to as a descending (A ^ M or M ^ B) or an ascending (B ^ M or M ^ A) series The three fixation points were the A, M, or B LED

The experiment lasted for twelve experimental sessions, six for each of two base durations At each base duration there were three pairs of two consecutive sessions, each pair featuring a single fixation point condition, A, M, or B There were three orders of assignment to the fixation conditions: A ^ M ^ B, B ^ A ^ M, and M ^ B ^ A In one of the two consecutive sessions, the series were ascending, in the other descending Overall, there were twelve session orders, based on the combination of 200 and 335 ms first or second, ascending and descending first or second, and three fixation point orders One participant was assigned to eleven of them, and two participants to one of them Each session began with six presentations of the base duration, following which there were four blocks of 60 trials, with a 15 s pause between the blocks There was

no feedback Within each session, there was only one fixation point, one base duration and one ascending or descending condition; but two height conditions

3.1.4 Data analysis For each participant and for each of the 24 conditions (2 base durations62 segments ö upper versus lower62 series ö ascending versus descending

63 fixation points ö A, M, or B), 8-point psychometric functions were constructed Each point on the psychometric function was based on 15 presentations The same model as in experiment 1 was used to fit the resulting curves

Because there are two base durations in the present experiment, the PSE was trans-formed into constant error (CE), ie the difference between the PSE and the base duration (200 or 335 ms); the more negative the CE, the longer the stimuli are judged

to be As well, the SD of the psychometric functions served to calculate the Weber fraction: WFˆ SD/base duration

3.2 Results and discussion

The pseudologistic functions generally described the data very well Out of the 24 experi-mental conditions, the lowest mean r2

value for the thirteen participants was 0.954, observed with a 200 ms base duration for the higher portion in the ascending direction when the fixation point was B The highest mean r2

value, 0.985, was obtained in the same combination of conditions, but with a 335 ms base duration

3.2.1 Perceived duration The mean results in each condition for perceived duration are reported in figure 4 An ANOVA on CE based on a 2626263 design with repeated measures on all factors (with Greenhouse ^ Geisser corrections when necessary) revealed no significant main effects However, the following interactions were sig-nificant: the segment6fixation point interaction (F2 24 ˆ 16:88, p 5 0:01, Z2

ˆ 0:58); segment6base duration interaction (F1 12 ˆ 12:80, p 5 0:01, Z2

ˆ 0:52); the series

6base duration interaction (F1 12 ˆ 5:95, p 5 0:05, Z2

ˆ 0:33); and the segment6 series6fixation point interaction (F2 24 ˆ 11:37, p 5 0:01, Z2

ˆ 0:49) As illustrated in figure 5, the direction of the segment and series effects varied with the fixation points

Because of series of significant interaction effects, three additional 26262ANOVAs, one for each fixation point, were conducted For the fixation point set on B, there were two significant main effects: segment (F1 12 ˆ 12:91, p 5 0:01, Z2

ˆ 0:52) and series (F1 12 ˆ 8:96, p 5 0:05, Z2

ˆ 0:43) The three double interactions were also significant: segment6series (F1 12 ˆ 5:95, p 5 0:05, Z2 ˆ 0:33); segment6base duration (F1 12 ˆ 12:60, p 5 0:01, Z2

ˆ 0:51); and series6base duration (F1 12 ˆ 6:48, p 5 0:05,

Z2 ˆ 0:35)

Two additional 2 (series)62 (segments) ANOVAs, one for each base duration, were conducted At 200 ms, the analysis revealed no effect of series, but the effect of segment (F1 12 ˆ 6:50, p 5 0:05, Z2

ˆ 0:35) and the series6segments interaction (F1 12 ˆ 11:31,

p 5 0:01, Z2

ˆ 0:49) were significant In the ascending series, the CE for the upper segment was 8.28 ms, and 5.12 ms for the lower segment; in the descending series, the

CE for the upper segment was 29.30 ms, andÿ9:56 ms for the lower segment At 335 ms, there was a significant segment effect (F1 12 ˆ 20:75, p 5 0:01, Z2

ˆ 0:63) and a signif-icant series effect (F1 12 ˆ 14:49, p 5 0:01, Z2

ˆ 0:55) The interaction effect was not significant The CE value was smaller with the lower than with the upper segment, and lower in the ascending series than in the descending series

, ,

, ,

, ,

,

, ,

45

40

35

30

25

20

15

10

5

0

ÿ5

ÿ10

ÿ15

ÿ20

20

15

10

5

0

ÿ5

ÿ10

ÿ15

ÿ20

ÿ25

ÿ30

ÿ35

Lower segment Upper segment

40 30 20

10 0 ÿ10 ÿ20 ÿ30

Figure 4 Mean constant error ( SE) for each experimental condition in experiment 2: (left) ascending; (right) descending; (top) 200 ms; (below) 335 ms.

For the middle point of fixation, the only significant effect observed was on the segment variable (F1 12 ˆ 5:34, p 5 0:05, Z2

ˆ 0:31) The CE was lower (longer per-ceived duration) with intervals presented in the lower portion of the visual field than

in presentations in the upper portion With the fixation point set on A, the ANOVA revealed significant segment effect (F1 12 ˆ 26:96, p 5 0:01, Z2

ˆ 0:69) The CE was larger (shorter perceived duration) with intervals presented in the lower portion of the

VF than in presentations in the upper portion No other effects were significant with either the M or A fixation point

3.2.2 Sensitivity The mean sensitivity results in each condition, expressed with the

WF, are reported in figure 6 An ANOVA according to a 2626263 design, with repeated measures on all factors, revealed that there was a significant base duration effect (Mˆ 0:243 and 0.207 at 200 and 335 ms, respectivelyöF1 12 ˆ 13:90, p 5 0:01,

Z2 ˆ 0:54) However, this effect interacted with the series effect (F1 12 ˆ 9:06,

p 5 0:05, Z2

ˆ 0:43) The series6fixation point interaction was also significant (F2 24

ˆ 11:46, p 5 0:01, Z2ˆ 0:49), as was the segment6series (F2 24 ˆ 4:83, p 5 0:05,

Z2 ˆ 0:29) and the segment6fixation point (F2 24 ˆ 14:74, p 5 0:01, Z2

ˆ 0:55) Three additional 26262 ANOVAs, one for each fixation point, were conducted For the fixation point set on B, there was no significant effect, but note pˆ 0:071,

Z2 ˆ 0:25, for the base duration effect, the WF being larger at 200 than at 335 ms For the M fixation point, besides the based duration effect ( pˆ 0:055), there is only

a segment6series significant effect (F1 12 ˆ 13:71, p 5 0:01, Z2

ˆ 0:53) While for the lower segment the WF was 0.25 in the ascending series and 0.19 in the descending series, the WF was reversed for the upper segment, and 0.20 and 0.23 in the ascending

,

,

,

, , ,

,

,

Lower segment Upper segment

Ascending series Descending series

20

15

10

5

0

ÿ5

ÿ10

ÿ15

11

10

9

8

7

6

5

4

3

2

1

0

ÿ1

ÿ2

ÿ3

Fixation point

Figure 5 Constant error ( SE) as a function of the fixation point for the lower versus upper segment conditions (upper panel) and for the ascending versus descending series (lower panel).

and descending series, respectively For the fixation point set on A, there was only a segment6base duration significant effect (F1 12 ˆ 8:84, p 5 0:05, Z2

ˆ 0:42) For the lower segment, the WF was nearly the same at 200 (0.228) and 335 (0.237) ms, but differed

in the upper segment (0.249 and 0.196, respectively)

4 General discussion

There were two dependent variables of interest in the present study, one related

to perceived duration and the other to the sensitivity for discriminating intervals The main theoretical questions addressed were related to the influence of visuospatial factors on perceived duration

4.1 Perceived duration

The general purpose of the study was to investigate the extent to which the perceived duration of single intervals marked by brief visual signals is linked to the spatial distance between signals Previous empirical investigations led to the conclusion that more space between signals results in longer perceived duration, which is referred to as the kappa effect The present work contributes to show that the influence of space on time perception is not that simple: more space between signals marking time does not necessarily lead to longer perceived duration

In experiment 1, the location of the signals (upper versus lower segments) in the visual field, and their direction (ascending versus descending), were randomised within blocks of trials Both location and direction exerted a significant effect on perceived duration, but the effect interacted with the height of the M signals In the case of direction, while the PSE remained relatively constant for the different height condi-tions in the ascending condition, the lower the M signals in the descending series were, the shorter was perceived duration However, lower M signals also means closer to

,

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

Lower segment Upper segment

Figure 6 Mean Weber fraction ( SE) for each experimental condition in experiment 2; (left) ascending; (right) descending; (top) 200 ms; (below) 335 ms.