Effects of interval duration on temporal processing in schizophrenia

Brain and Cognition 52 (2003) 295–301

www.elsevier.com/locate/b&c

Effects of interval duration on temporal processing in schizophrenia

Deana B. Davalos,* Michael A. Kisley, and Randal G. Ross

Denver VA Medical Center, University of Colorado Health Sciences Center, Denver, CO, USA

Accepted 29 April 2003

Abstract

Introduction: Temporal processing has received scant attention in the literature pertaining to cognitive deficits in patients with

schizophrenia. Previous research suggests that patients with schizophrenia exhibit temporal perception deficits on both auditory and

visual stimuli. The current study investigated the effects of interval manipulation to (1) replicate the original findings with a larger

sample and an increased number of trials (2) assess the degree to which both patients and controls can differentiate temporal changes

in a range of experimental interstimulus intervals, and (3) explore whether different interstimulus interval durations pose different

levels of difficulty for the patients with schizophrenia. Methods: Participants were asked to decide whether temporal intervals were

shorter or longer than standard intervals on a computer-based auditory temporal perception task. The standard interval remained

the same duration throughout the various tasks. The interstimulus interval separating the standard and experimental intervals varied

in the range of 500, 1000, or 3000ms. Data are presented for a sample of 16 patients with schizophrenia and 15 controls. Results:

Data suggest that patients with schizophrenia exhibit deficits in differentiating interval durations across all paradigms compared to

their control-group peers on a range of auditory tasks (p < :001). Conclusions: These results are consistent with a general temporaldeficit in schizophrenia. However, the roles of medication and localization are also addressed.

� 2003 Elsevier Science (USA). All rights reserved.

Keywords: Schizophrenia; Time perception; Timing; Interval discrimination

1. Introduction

Over the years, there has been increasing interest in

the ability to process temporal information, including

the relationship to clinical symptomatology and neural

dysfunction. Researchers have argued that temporal

processing deficits appear to be associated with specific

disorders, such as Parkinson�s disease and amnesia orwith specific types of brain damage, specifically cere-

bellum, basal ganglia, or frontal lobe insult (Artieda,Pastor, Lacruz, & Obeso, 1992; Casini & Ivry, 1999;

Harrington & Haaland, 1998; Heatherington, Dennis, &

Spiegler, 2000; Ivry & Keele, 1989; Nichelli, Clark,

Hollnagel, & Grafman, 1995; Rammsayer, 1993). One

argument that has arisen is that subtle differences in time

interval tasks may result in varied performances in

clinical populations. Researchers studying both animals

and patients with localized lesions have argued that the

* Corresponding author.

E-mail address: [email protected] (D.B. Davalos).

0278-2626/$ - see front matter � 2003 Elsevier Science (USA). All rights resdoi:10.1016/S0278-2626(03)00157-X

cerebellum may be associated with short-duration pro-

cessing while the perception of longer durations may belinked to the prefrontal cortex (Clarke, Ivry, Grinband,

& Roberts, 1996; Heatherington et al., 2000; Mangels,

Ivry, & Shimizu, 1998). Other studies have supported

the notion that the cerebellum is associated with rela-

tively automatic short-duration processing, but add that

it may be either the basal ganglia or cortex that take

over for longer durations (Hazeltine, Helmuth, & Ivry,

1997; Ivry, 1996; Ivry & Keele, 1989). Another hy-pothesis is that there may be an ‘‘internal clock’’ that

allows representation of real-time information that is

used to process all temporal information (Mangels et al.,

1998). Temporal processing deficits would then be at-

tributed to a general deficit in the area of the brain re-

sponsible for the ‘‘internal clock.’’ However, there is

little consensus regarding the localization associated

with the internal clock. Multiple researchers haveargued that the prefrontal cortex is not only involved in

the general capacity to process time, but it may be

responsible for our ‘‘internal clocks’’ (Nichelli, Alway, &

erved.

mail to: [email protected]

296 D.B. Davalos et al. / Brain and Cognition 52 (2003) 295–301

Grafman, 1996; Pastor, Artieda, Jahanshahi, & Obesa,1992). Others have argued that general temporal pro-

cessing deficits are associated with the cerebellum (Bu-

onomano & Mauk, 1994; Ivry & Keele, 1989; Jueptner

et al., 1995). Others believe that the basal ganglia is

likely responsible for the processing of the internal clock

and is involved in both short duration, largely automatic

processing of time and in longer intervals (Meck, 1996;

Rammsayer, 1993; Rammsayer & Lima, 1991). The ar-gument that both the cerebellum and basal ganglia are

involved in a coordinated timing system with a conver-

gence of central cortical control has also been asserted

(Gibbon, Malapani, Dale, & Gallistel, 1997).

Finally, others have argued that differences in tem-

poral processing performances during varying interval

durations may result from the employment of different

cognitive processes. Michon (1990) points out that de-pending on the particular task, temporal processing

measures may vary in the degree of abstraction and

complexity. Mangels et al. (1998) argue that longer du-

rations (e.g., 3 or 4 s) in interval comparison tasks may

have to be kept on-line via working memory and may be

particularly sensitive to frontal lobe deficits in working

memory versus reflecting temporal processing deficits.

Nichelli et al. (1996) suggest that the cerebellum may beinvolved in short interval duration estimation, however,

timing beyond 2 or 3 s may exceed intervals requiring

‘‘motor routines’’ and may reflect deficits in sustained

attention and/or strategy use. In both animal and hu-

man studies, the prefrontal cortex has been implicated in

working memory processes (Chein & Fiez, 2001; Gold-

man-Rakic, 1999; Mull & Seyal, 2001; Wall & Messier,

2001). Given that prefrontal dysfunction has historicallybeen associated with schizophrenia, it is possible that

particular impairments would be expected on longer

duration temporal tasks that may require working

memory (Goldman-Rakic, 1999; Goldman-Rakic &

Selemon, 1997; Perlstein, Carter, Noll, & Cohen, 2001).

One way to explore the possibility of widespread tem-

poral deficits due to ‘‘internal clock’’ difficulties versus

localized damage or the degree to which other cognitiveprocesses mediate performance would be to explore

temporal processing across a variety of conditions.

Schizophrenia is one clinical syndrome that has re-

ceived limited attention regarding temporal processing.

Previous neuropsychological research has often focused

on deficits pertaining to ‘‘executive functioning’’ (e.g.,

attention, working memory, and planning) (Stern &

Prohaska, 1996; Szeszko et al., 2000). These deficits arethought to be related to frontal lobe dysfunction and

have historically been associated with the daily living

difficulties patients with schizophrenia face (Green,

Kern, Braff, & Mintz, 2000). Relatively few researchers

have addressed the possibility that deficits in everyday

living may instead be affected by difficulties with tem-

poral processing.

Some have argued that the ability to process timemay have far reaching effects in a person�s daily livingand quality of life. Tracy et al. (1998) have discussed the

role of time estimation in understanding ‘‘warning sig-

nals’’ that predict later events. Others have presented

temporal dysfunction as a deficit that may affect a wide

range of behaviors, such as sequencing motor behavior

and planning time-based events (Volz et al., 2001). More

obvious problems associated with temporal processingdeficits include difficulty estimating how long tasks will

take or trouble scheduling sequential events appropri-

ately. In schizophrenia, difficulties with these endeavors

along with other daily living difficulties may be partially

explained by deficits in processing time rather than

traditional cognitive deficits associated with schizo-

phrenia such as executive functioning deficits and

problems with working memory (Perry et al., 2001).In the past, research focusing on schizophrenia and

temporal processing deficits has been limited due to very

small sample sizes and the lack of consensus in tasks

described as ‘‘temporal processing’’ measures. Some

temporal processing experiments utilize what would be

considered estimation tasks and perception tasks to-

gether as a measure of temporal processing, rather than

breaking up the tasks to better clarify the processes. Afurther limitation is the degree of nontemporal infor-

mation that has been included in the temporal process-

ing tasks utilized. Earlier research suggested that

temporal perception tasks often required the subject to

attend to nontemporal information, which likely af-

fected the temporal processing (Poynter & Homa, 1983).

Many of the studies around the 1970s required subjects

to estimate duration of words and nonwords (Avante,Lyman, & Antes, 1975; Thomas & Weaver, 1975; Warm

& McCray, 1969). Duration judgments were affected by

the familiarity of the word, suggesting that subjects

attend to other nontemporal qualities of information

in their time estimations.

The present study attempted to limit the nontemporal

qualities of the task and subjects were exposed to only

one stimulus that was 50ms in duration and 1000Hzthroughout the entire study. Subjects had to respond to

the stimuli, which introduces the possibility of mediating

cognitive factors. However, it has been noted that re-

sponding versus producing time may be a better mea-

surement of perceptual processing versus perception/

attentional processing (Fortin & Rousseau, 1987). In

addition, it has been hypothesized that when intersti-

mulus intervals (ISIs) are expanded beyond about 2 s,there is a loss of coherence between successive events,

rather each stimuli becomes processes as an independent

event (Vos & Ellerman, 1989). Mates, M€uuller, Radil,and P€ooppel (1994), also found a breakdown in theability to time and synchronize behavior when ISIs

reached about 2400ms. The authors suggest that the

short-term memory trace in temporal processing of the

D.B. Davalos et al. / Brain and Cognition 52 (2003) 295–301 297

preceding stimuli may begin to fade out after about 2–3 s. The paradigm utilized in the current study addresses

the possibility that longer intervals may affect temporal

processing performance by including longer intervals in

the selected ISI durations.

An initial study attempted to provide a preliminary

examination of a cross modal measure of temporal

perception in schizophrenia (Davalos, Kisley, & Ross,

2002). Subjects were presented with two time intervalsthat differed by only tens of milliseconds. Using a

forced choice paradigm, differences were noted between

groups on tasks of both auditory and visual temporal

perception.

The current study investigates the effects of interval

manipulation on performance between individuals with

schizophrenia and controls. Both patients and controls

are exposed to a range of experimental interstimulusintervals. Nontemporal variables are limited by utilizing

the same stimuli across conditions. This study explored

whether different interstimulus interval durations pose

different levels of difficulty for the patients with schizo-

phrenia.

2. Method

2.1. Participants

Subjects consisted of 15 subjects (nine males, six fe-

males; age range¼ 20–50 years) who met DSM-IV

(American Psychiatric Association, 1994) criteria for

schizophrenia, confirmed via a structured interview

(Endicott & Spitzer, 1978). Given that the use of typicalneuroleptics may be associated with adverse effects on

timing tasks (Gibbon et al., 1997; Meck, 1983), only

subjects treated with atypical neuroleptics were selected.

Fourteen subjects were treated with either olanzapine or

risperidone, one subject was unmedicated.

Sixteen controls (four males, 12 females; age range

23–58 years) were recruited through advertisements.

Respondents were screened for psychiatric histories.Individuals were excluded for a current diagnosis of

major depression, substance abuse, neurological disor-

ders, head trauma, or for any personal or first-degree

family member history of psychosis. All subjects gave

written consent for participation, as approved by an

appropriate Institutional Review Board, and were paid

$30 for participation.

Mean years of age�SD at the time of testingwere 41.24� 8.45 for patients with schizophrenia and38.50� 12.08 for control subjects; t ¼ :74, p ¼ :47.

2.2. Procedure

Auditory time perception was measured using a

method introduced by Ivry and Keele (1989). In short,

subjects compare successive intervals of two pairs oftones. The first pair of tones is used as a ‘‘standard’’

interval. Each tone is 50ms in duration, 1000Hz, and

the initial time between the standard pair is consistently

400ms. Either 500, 1000, or 3000ms after the initial

pair, the subject hears a second experimental pair of

tones. This second interval is called the ‘‘experimental’’

interval. On half the trials, the experimental interval is

shorter than the 400ms first interval, either 310, 340,355, or 370ms in duration. On the other half of trials,

the experimental interval is longer than the 400ms first

interval, either 430, 445, 460, or 490ms in duration. The

subjects are presented with 20 trials per experimental

interval (e.g., 310ms) per interstimulus interval (ISI)

duration (e.g., 1000ms). The presentation order for the

experimental interval duration was randomized over 160

trials per ISI. The presentation order of stimuli was 80trials of 1000, 500, and 3000ms, a short break, and then

the same order repeated. The subject was asked to

manually respond by pressing the ‘‘S’’ key if the exper-

imental interval was ‘‘shorter’’ than the standard inter-

val and the ‘‘L’’ key if the experimental interval was

longer than the standard interval. The presentation of

each new trial was contingent on a response to the

previous trial. Therefore, all participants responded toall trials. Each subject performed an initial control task

to assess the participant�s hearing and appropriate

volume for the task.

Four individuals with schizophrenia and three con-

trols had their scores averaged from only one of the two

trials (80 comparison intervals rather than 160) due to

their inability to respond using the correct keys consis-

tently. Two of those individuals with schizophrenia hadto have their 3000ms trials completely dropped since

they had not completed either of the two trials correct.

Therefore, the data presented for the 3000ms ISI is

based on 16 controls and 13 patients.

2.3. Data analysis

For each subject, the number of errors was recordedfor each of the experimental intervals at each of the

ISI�s. Groups were compared on the mean percentage oferrors at each experimental interval duration (e.g.,

310ms) within each ISI (e.g., 3000ms). Repeated mea-

sures ANOVAs were computed for mean percentage of

errors, with ISI and experimental interval as within-

group factors, and diagnosis as between group factor.

Two-tailed t test post hoc comparisons were conducted.

3. Results

A repeated measures ANOVA with ISI as indepen-

dent factor indicated a significant difference between

groups on total errors committed, across all

Fig. 3. Mean percentage of errors during the 3000-ms interstimulus

interval duration for 16 controls (circles) and 13 patients with

schizophrenia (squares). The vertical centerline represents the standard

interval.


experimental intervals, during the auditory perceptiontask (F ¼ 20:50; p < :001). Overall, ISI duration sig-nificantly affected performance (F ¼ 7:67; p ¼ :001). Inparticular, more total errors were committed at the

500ms ISI than either the 1000 msec ISI (t ¼ 4:79;p < :001) or 3000ms ISI tasks (t ¼ 2:26; p ¼ 0:032). Nosignificant difference in errors was noted at the 1000ms

ISI compared to the 3000ms ISI (t ¼ 1:24; p ¼ 0:22).No significant group-by-ISI interaction existed(F ¼ 1:16; p ¼ 0:32), suggesting that patients exhibiteda general impairment in performance across all ISIs.

Regarding the effects of experimental interval dura-

tion, the ANOVA revealed a significant effect of exper-

imental interval duration (e.g., 310ms) on performance

overall across all ISIs (p < :001). In general, perfor-mance declined when the experimental interval was most

similar to the standard interval. However, there were nosignificant group-by-interval duration interactions for

any ISI, suggesting that patient group is uniformly im-

paired across all interval durations. The differences in

performance between groups across all experimental

intervals during all three ISI duration conditions are

displayed in Figs. 1–3. Mean percentages of errors for

the two groups are displayed in Table 1.




interval.




interval.

4. Discussion

Previous research suggested that patients with

schizophrenia might have temporal processing deficits,

at least with regards to specific temporal intervals(Davalos et al., 2002). In the current study, one goal was

to replicate the original pilot study with a larger sample

and an increased number of trials. Similar to the first

study, patients with schizophrenia exhibited temporal

processing deficits across the array of experimental in-

terval durations. Schizophrenic�s performance appearsto follow the same curve of performance that the con-

trols exhibit, however the patients are consistently im-paired across the different conditions and experimental

interval durations.

One question that arose from the previous study re-

lated to the possibility of a general temporal deficit

versus a temporal deficit specific to the single interval

duration that was assessed (1000ms). Previous re-

searchers have found that specific localized brain dam-

age may contribute to distinct temporal deficits ratherthan general temporal processing dysfunction. Specifi-

cally, group differences in cerebellar or basal ganglia

functioning were hypothesized to result in poorer per-

formance on short-duration perception, whereas frontal

lobe abnormalities would likely result in specific im-

pairment on tasks requiring discrimination of longer

interval durations in the seconds range (Heatherington

et al., 2000; Mangels et al., 1998). In the initial study,only the 1000ms ISI was assessed. The current study

assessed a range of intervals in an attempt to rule out the

possibility that the differences between groups that were

initially cited resulted from a specific localized dys-

function associated with the 1000ms ISI duration.

A further hypothesis was that the different ISI dura-

tions might pose different types of problems for the

schizophrenia group. As can be seen in Fig. 4, all of theISI durations appear to be more difficult for the

schizophrenia group compared to the controls. While it

Fig. 4. Mean percentage of errors during each of the ISIs.

Table 1

Mean (SD) percentage of erroneous trials as a function of ISI and interval durations

Experimental

interval

duration

ISI

500ms 1000ms 3000ms

SZ Control SZ Control SZ Control

310 17.0��(16.9) 4.1 (8.2) 8.3� (11.9) .9 (2.7) 14.0 (21.9) 1.9 (5.4)

340 30.7�� (20.2) 7.8 (8.6) 14.7� (14.9) 4.1 (8.0) 16.2�� (7.4) 1.9 (3.6)

355 29.0�� (19.4) 13.4 (13.9) 20.0�� (14.3) 4.7 (4.6) 14.2�� (12.1) 3.8 (5.6)

370 29.0� (17.6) 17.2 (10.6) 27.3�� (17.8) 12.5 (9.5) 28.5�� (14.6) 10.0 (6.3)

430 38.7�� (17.1) 22.5 (16.0) 35.7�� (15.9) 20.3 (16.3) 34.2 (20.7) 27.2 (13.7)

445 28.0�� (16.3) 14.7 (12.0) 20.3 (17.1) 11.9 (12.5) 25.4�� (18.2) 6.6 (8.3)

460 27.7� (18.3) 14.0 (12.0) 20.3�� (7.2) 11.6 (10.3) 30.8�� (19.7) 11.3 (11.3)

490 16.7 (13.0) 8.4 (9.4) 14.3�� (11.2) 3.8 (5.9) 20.0�� (22.5) 4.7 (10.1)

* Significantly different from control group ðp6 :05Þ.** Significantly different from control group ðp6 :01Þ.*** Significantly different from control group ðp6 :001Þ.


was noted that the 500ms interval duration was more

difficult overall, the increased difficulty does not appear

to be specific to schizophrenia. It is possible that the

more distinct deficit noted at the 500ms interval may bedue to mediating cognitive factors that are associated

with processing short interval durations. One cognitive

process that may play a role in the ISI deficit seen at

500ms is backward masking. The idea of backward

masking in temporal perception tasks has been analyzed

(Cantor & Thomas, 1976; Idson & Massaro, 1977;

Massaro & Idson, 1976, 1978). Massaro (1975) theo-

rized that an auditory stimulus is stored in preperceptualmemory and if a second auditory stimulus is presented

before the processing is complete, the representation of

the first auditory stimulus is lost and processing is ter-

minated. While the typical duration that has been as-

sociated with the ‘‘preperceptual’’ memory or short

auditory store is 200–300ms (Cowan, 1984; March et al.,

1999), it is possible that the difficulties noted on the

500ms ISI may be explained, in part, due to backwardmasking effects. This argument would be in accord with

research finding that backward masking causes impaired

performance on cognitive tasks. Regarding the role of

backward masking specifically in schizophrenia, re-

search findings have been mixed with some finding

deficits in schizophrenia and other stating that no sig-

nificant differences exist (Kallstrand, Montnemery,

Nielzen, & Olsson, 2002; March et al., 1999). It appears

that forward masking may be more difficult for this

population while deficits on simultaneous and backward

masking appear to be more task-specific than generally

impaired (McKay, Headlam, & Copolov, 2000). Simi-larly, differences have been noted regarding the regions

associated with the different types of masking. Back-

ward masking has been linked to central nervous net-

work systems in the frontal cortical areas (Kallstrand

et al., 2002). This lack of significant differences between

groups on the 500ms ISI and on the 3000ms ISI would

suggest that temporal processing deficits in schizophre-

nia do not appear to be further exacerbated by frontalcortical deficits as we once hypothesized. It would seem

that if frontal cortex areas were largely involved in

temporal processing, you would expect to see increased

difficulty relative to the 1000ms task on the two tasks

that may be affected by backward masking and working

memory difficulties. It was hypothesized that the longer

duration ISI (3000ms) and the shorter duration ISI

(500ms) might require additional cognitive processesthat could selectively impair the patients� performances.While the shorter duration appeared to be more difficult

for everyone, neither ISI duration associated with

frontal cortex processing posed specific problems for the

individuals with schizophrenia.

The results of this study suggest that patients with

schizophrenia exhibit general deficits in auditory tem-

poral perception. It was shown that whereas controlscould differentiate minute differences in duration (e.g.,

45ms), patients with schizophrenia continued to make

errors up to 150ms. These findings are consistent with

our previous study and suggest that rather than a lo-

calized temporal deficit, patients with schizophrenia

possess a general timing dysfunction. However, there are

limitations that may be addressed in future studies. The


effect of psychopharmacological intervention on tem-poral processing tasks is not well understood. Tradi-

tonal neuroleptics have been found to increase

variability on temporal tasks and effect ‘‘clock speed’’ in

both animal and human studies (Gibbon et al., 1997;

Meck, 1996). However, little is known about the effects

of atypical medications, particularly olanzapine on

temporal tasks. It should be noted that recent studies

have found that olanzapine effects other types of cog-nitive tasks and results in structural changes in the basal

ganglia and cerebral activation changes in the cerebel-

lum and prefrontal regions, all areas that have both been

hypothesized to be involved in temporal processing

(Andersson, Hamer, Lawler, Mailman, & Lieberman,

2002; Stephan et al., 2001). In particular, olanzapine was

found to ‘‘normalize’’ cerebellar functional connectivity

in only the right, but not left cerebellum, during a fingertapping task. Studies assessing the effects of olanzapine

on these structures and on similar cognitive tasks have

been rare and have resulted in inconsistent findings.

However, given that olanzapine has been shown to effect

the majority of areas associated with temporal process-

ing, it should be noted that the between group differ-

ences described in the current study can not be ruled out

as being related to olanzapine use. Future studies shouldaddress this limitation by including neuroleptic naive

patients to rule out the effects of both typical and

atypical medications.

In addition, there is little consensus regarding the

localization of the internal clock. In the current study,

we asserted that more significant impairment on the

longer ISI (e.g., 3000ms) versus the shorter interval

tasks might shed light on the use of mediating cognitivevariables associated with decision making in responses

and the role of the prefrontal cortex. Whereas, signifi-

cant differences across all variables may reflect a general

timing deficit. The current findings suggest that patients

with schizophrenia exhibit timing deficits across all in-

terval durations. The deficits noted do not support the

idea that the frontal cortex-related ISIs are particularly

problematic for individuals with schizophrenia. Fur-thermore, while being cognizant of the possible con-

founding effects of medication, it appears that the idea

of a general timing deficit may best describe the tem-

poral processing dysfunction noted in this population.

Future studies addressing different decision making

strategies or response biases between the groups may be

useful in understanding the cognitive processes involved

in behavioral measures of temporal processing. Addi-tionally, research utilizing complementary methods such

as electrophysiology and functional neuroimaging are

planned to help clarify the facets of temporal processing

and the physiological etiology of temporal dysfunction.

While we posit that there may be a general timing dys-

function in this population, the physiology of this dys-

function is poorly understood. As additional studies

suggest structural and functional abnormalities inschizophrenia in areas including the cerebellum and

basal ganglia, it appears that a number of brain struc-

tures could be contributing to the temporal dysfunction

noted in this population. Future studies addressing these

localization questions and the types of cognition in-

volved in temporal processing may lead to greater un-

derstanding of the physiology and neuropsychology of

temporal deficits associated with schizophrenia.

Acknowledgments

This research was partially supported by the follow-

ing grants: Developmental Psychobiology Endowment

Fund and by Public Health Services Grants MH56539

and MH152442.

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