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Journal of Clinical and Experimental Neuropsychology Temporal Preparation Strategy may Inflate RT Deficit Louis Bherer1, Sylvie Belleville2,3, and Brigitte Gilbert2 1Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA, and 2Institut Universitaire de Ge´riatrie de Montre´al, Montre´al, Que´., Canada, and 3Department of Psychology, Universite´ de Montre´al, Montre´al, Que´., Canada Twelve patients with Parkinson’s disease (PD) and 12 age-matched controls completed a visual reaction time(RT) task to assess the effect of temporal parameters on response preparation. Simple and choice RTconditions were presented in separate blocks. In both conditions, preparatory intervals of various durations(1, 3 and 5 s) were introduced between an auditory warning signal and the visual target. Within a block oftrials, intervals varied randomly. The results indicated that PD patients responded slower than controls inboth task conditions. Also, there was evidence for preparation in both groups, as RT decreased withincreasing intervals. A three-way interaction indicated that PD patients’ RT was longer than that of controlsat the shortest interval in simple RT. This suggests that PD patients show a different pattern of temporalresponse preparation and that this may contribute to their deficit on RT tasks.
Parkinson’s disease (PD) is characterized by poral information to prepare a simple forthcom- slowness in movement initiation (akinesia), trem- ing response in reaction time tasks. Preparatory ors and reduced movement execution. These processes refer to the ability to develop and symptoms have been associated with a degen- maintain an optimal processing state prior to eration of neurons that produce dopamine in the execution of movements. Preparing a res- the substantia nigra, which in turn results in a ponse involves activating the appropriate action reduction of dopamine in the striatum and the schemas in advance and maintaining their activa- putamen (Jahanshahi & Frith, 1998). Reaction tion until the stimulus occurrence (Stuss, Shallice, time (RT) paradigms have been used extensively with PD patients to assess psychomotor symp- It has long been recognized that response Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 toms. The majority of studies have reported preparation has a major impact on performance in increased RTs in PD patients relative to control RT tasks (Niemi & Na¨a¨ta¨nen, 1981). One way in participants (see Gauntlett-Gilbert & Brown, which preparatory effects manifest themselves is 1998 for a review). It has been proposed that RT through comparison of performance in appro- paradigms might help to illuminate the putative priately matched simple and choice RT tasks.
relation between the cognitive impairments and Choice RT involves a larger number of processes deficits in the control of voluntary actions in PD because it requires, in addition to stimulus (Berry, Nicolson, Foster, Behrmann, & Sagar, detection and response execution, stimulus dis- 1999). The present study addresses this issue by crimination, response selection and in most cases, examining the ability of PD patients to use tem- maintaining in memory the target and response Address correspondence to: Louis Bherer, Beckman Institute for Advanced Science and Technology, University ofIllinois at Urbana-Champaign, Urbana, IL 61801, USA. E-mail: [email protected] for publication: January 27, 2003.
alternatives. Furthermore, in simple RT tasks, participants know in advance the exact response that they will have to produce and thus specific Another important source of discrepancy might preparation can also occur. Thus, specific pre- be the absence of consideration of time para- paration partially accounts for faster RTs in meters in the majority of studies comparing simple and choice RTs in PD. This point is important because the magnitude of the prepara- simple and choice RTs suggest that preparatory tory effect in RT tasks depends on both specific deficits exist in PD. The major empirical and nonspecific preparation. Specific preparation argument for this hypothesis is the presence in occurs when a predetermined response is asso- PD patients of a larger deficit in simple than ciated with a specific stimulus, as in simple RT.
Choice RT (Bloxham, Mindel, & Frith, 1984; Nonspecific or temporal preparation refers to the Evarts, Tera¨va¨inen, & Calne, 1981; Goodrich, synchronization of an action in time and is based Henderson, & Kennard, 1989; Sheridan, Flower, on signal expectancy and time uncertainty. Con- & Hurrel, 1987). A failure to implement specific trary to specific preparation, temporal preparation preparation of the response required in the simple has a major impact in both simple and choice RT.
RT task may account for the smaller advantage for Importantly, nonspecific preparation is dependent simple over choice RT in PD patients relative to upon the temporal characteristics of the design.
control participants. This failure to engage in The preparatory interval (PI), which is the specific preparation has been proposed to arise interval between the warning signal and the target, from impairment in the attentional control pro- is a determinant factor of temporal preparation cesses mediated by the frontal lobe (Gaunlett- (Niemi & Na¨a¨ta¨nen, 1981; Bertelson, 1967).
Gilbert & Brown, 1998; Goodrich et al., 1989).
When PIs vary unexpectedly across trials, stimu- This is in line with Fuster’s view (Fuster, 1999) lus likelihood increases with time and temporal that the prefrontal cortex comes into play to preparation involves both temporal and probabil- organize and plan the temporal structure of ity information. For instance, if PIs of 1, 2 and 3 s occur randomly in a block of trials, the probability However, some studies have not reported clear that the signal will occur after 1 s is 1/3, then it evidence of specific preparation impairment in increases to 1/2 at 2 s and it is perfect at 3 s.
PD based on the comparison of simple and choice Because subjects prepare their response in line RTs. In these studies, persons with PD are found with the increased probability of occurrence of the to be slower in choice than simple RT tasks target, RT typically decreases as the PI increases relative to control participants (Cooper, Sagar, (Na¨a¨ta¨nen & Merisalo, 1977; Polzella, Ramsey, & Tidswell, & Jordan, 1994; Jahanshahi, Brown, & Bower, 1989). For this effect to be observed, PIs Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 Marsden, 1992a). There are at least two major need to be distinct (not too close in time) and factors that could lead to a larger RT impairment embedded in a temporal window that can be used effectively by participants. The variable PI design One is related to the fact that choice RT is more is interesting because it is similar to the conditions complex than simple RT, as mentioned earlier.
of preparation that participants have to face in The greater complexity of the choice RT task their daily lives, where actions are performed in a relative to the simple RT task may be particularly changing environment in which event occurrence critical for PD patients who exhibit frontal is rarely perfectly predictable. Unfortunately, impairments (Pate & Margolin, 1994), which is previous studies with PD patients have used PIs often the case (Gotham, Brown, & Marsden, that do not yield optimal preparation in control 1988). However, this interpretation cannot easily participants and this could account for absence of account for the afore mentioned findings of a larger impairment in simple relative to choice RT Studies that have shown an advantage of simple found in a fairly large number of studies and for over choice RT in PD or a larger deficit in PD in the finding of a reduced effect of a secondary task choice RT, suggesting normal preparation, have TEMPORAL PREPARATION AND RT IN PARKINSON’S DISEASE sometimes used short PI delays embedded in a very cognitive and motor portion of the global RT. This short time window (e.g., 0–250–500–2500 ms in was done by measuring response time from the Jahanshahi et al., 1992a). These are conditions that release of a home key. This technique, also used don’t promote optimal preparation in control by Jahanshahi et al. (1992a) with PD patients, is participants and that are thus less likely to yield of particular interest with a clinical population group differences with PD patients. In contrast, suffering from slowness in movement execution.
studies that showed the smallest advantage of It was expected that the impact of preparation simple over choice RT in PD, supporting a specific would specifically affect the pre-execution stages preparation deficit, typically used long and distinct of response processing or the time taken to release PIs over a large time range (e.g., 1500 and 2500 ms the home key but not the execution time or the in Sheridan et al., 1987; 1500 and 3000 ms in time to reach the response key (Bherer & Goodrich et al., 1989; 1800 and 2500 ms in Evarts Belleville, 2002; Jahanshahi et al., 1992a). Finally, et al., 1981). Using temporally distinct PIs the impact of attentional control and maintenance may have facilitated the use of temporal param- deficits on the response preparation of PD patients eters to enhance specific preparation in control was explored by assessing the relation between participants, thus facilitating emergence of group performance on span and executive tasks and PD patients exhibit larger RT deficits as a function of response (Brown, Jahanshahi, &Marsden, 1993) or stimulus uncertainty (Cooper et al., 1994). It is of major interest to investigatewhether these patients will show a specific preparation deficit in task conditions that involve Participants were 12 patients who received a diagnosis of both temporal and probability information, such Parkinson’s disease from a neurologist specializing inmovement disorders and 12 healthy matched controls.
as with variable PI intervals. Analyzing the All participants were Francophone Canadians living in pattern of performance across PI values in a the Montre´al community. All but 1 participant were variable PI design will allow for an assessment of native Francophone speakers. All control participants participant’s ability to use temporal and prob- were in good health and none of them had undergone ability information to prepare a response. Unfor- surgery or suffered from psychiatric disorders in the few tunately, in many studies that have shown a years prior to testing. They had no history of neurological preparatory deficit in PD patients, RT was pooled disease and did not take any medications known to affectcognitive functions. None of the patients were institu- over PI values and the PI effect was not assessed tionalized or had suffered from stroke, head injuries, (Evarts et al., 1981; Goodrich et al., 1989; psychiatric disorders or other neurological problems.
Severity of the disease was measured by the Hoehn and Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 The goal of the present study was to under- Yahr scale (1967). Three patients were in Stage 1, 4 in stand more clearly the relation between temporal Stage 2 and 5 in Stage 3. Akinesia was the predominant and specific preparation in PD patients using symptom for 5 PD patients whereas bradykinesia was parameters that were most likely to yield temporal predominant for 3 others. Four patients suffered fromboth types of symptoms. For many patients, activities of preparation in typical participants (Bherer & daily living were carried out slowly with assistance. A Belleville, 2002). The experiment compared motor exam substantially revealed difficulty arising choice and simple RT conditions in a variable PI from a chair, stooped posture, postural instability and design with three relatively long and well-defined bradykinesia. As shown in Table 1, the mean duration of PIs (1, 3 and 5 s). It was expected that analyzing the disease was 8 years, with a standard deviation of 5 the pattern of performance across PI values might years. All patients were on stable anti-parkinsonian provide informative data regarding PD patients’ medication at the time of testing. Two of them weretaking anticholinergic drugs and dopamine agonists, capacity to modulate their level of specific while the others were taking L-Dopa with or without (simple RT) and nonspecific (choice RT) prepara- tion. The impact of temporal parameters on the Demographic characteristics and scores on clinical response process was assessed separately for the tests for both the PD and the control groups are shown Table 1. Groups’ Mean for Demographic Characteristics and Test Scores.
Note. Standard deviation (SD) along with maximum and minimum [min.–max.] values are presented in brackets.
No significant difference was observed between the groups.
in Table 1. To exclude persons with dementia, all the home key and pressing the right response key as participants completed a short mental examination quickly as possible. Half-way through the block, they (MMSE from Folstein, Folstein, & McHugh, 1975) and were instructed to respond to the left button. In the the Mattis Dementia Rating Scale (Mattis, 1976). As choice RT condition, the black circle occurred ran- shown in Table 1, PD patients and controls performed domly either to the right or left of the centre of the within the normal range on these examinations. The screen and participants were asked to react to the mean MMSE score was 29 in both groups and, mean imperative signal by quitting the home key and pushing score for the Mattis Dementia Ratting Scale was 139 down the corresponding response key to the right or left and 140 respectively for PD and control participants.
of the home key. In both the simple and choice RT None of the participants showed clinical signs of conditions, PIs were 1, 3 and 5 s in duration. The depression (DSM-IV, 1994). Nevertheless, as depres- proportion of each PI value was equated in each block sive symptoms are often observed in PD patients, the of trials. They were presented in random order. After 5 Geriatric Depression Scale (GDS; Yesavage et al., practice trials on each task, a first block of 30 trials was 1982) was used as an objective measure of depressive completed in simple RT and a first block of 60 trials was symptoms. PD patients showed slightly more depres- completed in choice RT. Both the simple and choice sive symptoms than normal controls, a difference that RT conditions were conducted twice within a single experimental session and thus the total number ofcompleted trials was 60 in simple RT (20 at each PI)and 120 in choice RT (40 at each PI). The second blocks were separated from the first by a 30–40-mindelay during which the participants completed other unrelated experimental tasks (see Gilbert, Belleville, The experiment was under the control of Psyscope 1.0.1 Bherer, & Chouinard, submitted). An ANOVA invol- (Cohen, MacWhinney, Flatt, & Provost, 1993), running ving Block (1 and 2), Condition (simple vs. choice) and Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 on a MacIntosh PowerPC. Participants started the trials PI indicated neither an effect of block on initiation time, and gave their response on a three-button response box nor any interaction with group. Thus, the data were (Psyscope ButtonBox). This device allows for the mea- pooled over the two blocks for subsequent analyses.
surement of response initiation and execution time tothe nearest millisecond. The three buttons of differentcolours (left to right; red, yellow and green) were arranged linearly on a 17 cm by 13 cm panel separated Psychomotor and motor measures The neuro- by 3 cm. Participants completed simple and choice RT psychological assessment involved assessment of tasks in which each trial was initiated by pressing the motor and psychomotor abilities, short-term memory central button of the response box after a warning signal and executive functions. These data were presented (a 1000-Hz tone at 75–80 dB). Participants were re- and discussed elsewhere (see Gilbert, Belleville, quired to hold down the button until the occurrence of Bherer, & Chouinard, submitted) and thus only the the imperative signal, which was a black circle 4 in. in believed to be of particular importance for the present In the simple RT condition, the black circle study will be discussed here. Of major concern for appeared in the centre of the screen and participants our purposes, the participants completed a psycho- were asked to react to the imperative signal by quitting motor task (DSST from the Ottawa-Wechler Battery, TEMPORAL PREPARATION AND RT IN PARKINSON’S DISEASE 1953) and a motor task (Purdue Pegboard). In the DSST given two additional trials. Testing ended when task, the participants were presented with a key on participants failed to correctly report at least two which each number from 1 to 9 is matched with a sequences of squares of a given length. The span was geometrical symbol. The key was printed on the bottom defined as the longest sequence correctly reported on portion of a sheet of paper. On the upper portion, a 50% of the trials on a sequence length.
series of numbers were presented alone and the The alphabetical recall test is intended to measure a participant’s task was to write down the geometric specific executive function, that is, the ability to symbol corresponding to each number. The partici- manipulate information in working memory. The pant’s score is the total number of items completed critical aspect of the alphabetical procedure consists in 90 s. The Purdue motor task (Purdue Research of comparing two conditions of immediate word recall: Foundation, 1948) required putting round pegs into a a direct condition in which items are recalled in the series of holes aligned vertically on a board. Partici- same order as presented, and an alphabetical condition pants’ score consisted of the total number of pegs in which participants are asked to recall the words in placed in 30 s with the left hand, the right hand and both alphabetical order (according to the first letter of the word). This task has been used by Belleville, Rouleau,and Caza (1998) to investigate working memoryfunctioning in normal older adults. The words used for this task were monosyllabic. French words were selected to meet the criteria for frequency and All participants also completed a digit span, a word imaginable substantives, and were unambiguous with span and a visuo-spatial span task to assess short-term respect to the print-to-sound correspondence of their retention capacity. The digit span procedure was an first letter. Words in a sequence never began with the adapted version of the digit forward subtask of the same letter and shared no phonological or semantic Weschler Adult Intelligent Scale (WAIS), presented in similarity. Sequence length was also controlled for, detail in Belleville, Peretz, and Malenfant (1996). The taking into account the manipulation requirement of participants recalled orally sequences of digits that the sequences of words in the alphabetical condition.
were drawn randomly from 1 to 9. The digits were read The number of words to be recalled in each condi- aloud by the examiner. Four sequences of a given tion corresponded to the participant’s word span as number of digits (starting with two numbers) were measured previously. Participants completed 20 differ- available. If participants correctly recalled the first two ent sequences (10 in the direct condition and 10 in the series, sequences of one item longer were administered.
alphabetical condition). The proportion of correct The span corresponded to the longest sequence recalled items recalled was calculated. The following equation correctly on at least half of the trials. Moreover, as part expresses the performance on alphabetic recall when of an alphabetical recall test (described below), short-term memory capacity is taken into account: participants also completed a word span task. Short- Direct recall À Alphabetic recall/Direct recall. This term memory capacity for words was assessed using a measure is considered to reflect one’s ability to classical span measure. Again, the span was defined as manipulate information in working memory.
the longest sequence recalled correctly on at least 2/4 ofthe trials of a given sequence length. The visuo-spatial Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 span task is a modified computed version of the Corsi span. An array of 16 white squares (18 mm  18 mm)with a black border appeared on the computer screen.
Two dependent variables were considered: initia- Stimuli were localized semirandomly and half of them tion time and execution time. Initiation time (IT) were situated on each side of the screen. Square was measured as the time elapsing from the sequences of varying length (from 2 to 8 items) wereconstructed with stimuli randomly selected from the occurrence of the imperative stimulus to the pool of 16 squares with the only restriction that no moment when participants removed their finger square could be used twice in a same trial. For each from the home key. Execution time (ET) was the length, four different sequences were created. White time taken to move from the home key to the squares darkened sequentially for 2 s before returning response button. Response times were compiled to their original appearance. The inter-stimulus interval for correct answers only, and anticipate responses was 250 ms. Participants’ task was to point at squares in (i.e., leaving the home key before the imperative the same order as they were presented. The length ofthe sequence began with two squares and was increased signal) were rejected. Trials were not included in by one item every two trials. However, if an error the analyses if IT was shorter than 100 ms, or if occurred on one of these two trials, participants were the global response time (IT þ ET) was longer than 3000 ms. A trial was also excluded if IT was RT conditions. The interaction was rather due to a two standard deviations above or below a partici- larger difference between simple and choice RTs pant’s average RT performance. On average, this when participants were responding to the left resulted in excluding 4.9% of the trials in simple (Simple, 361; Choice, 430; p < .001, 2 ¼ 0.74) RT and 4.3% in choice RT for the PD participants, than when responses were given to the right and 6.3% and 6.5% in simple and choice RT (Simple, 368; Choice, 424; p < .001, 2 ¼ 0.66).
Importantly, this effect did not interact with theGroup factor.
reached significance, F(2, 44) ¼ 3.39, p < .05, 2 ¼ 0.13. To understand this interaction more The results of both task conditions are shown for fully, an ANOVA was performed separately on PD and control participants in Figure 1. It appears choice and simple RT. On the choice RT, PD that in both groups and in both conditions, RT was quicker as PI increased. In addition, the PI effect F(1, 22) ¼ 13.7, p < .001, 2 ¼ 0.38, and IT in the simple RT condition was larger in PD significantly decreased with PI, F(2, 44) ¼ 6.23, patients than in the control participants.
p < .01, 2 ¼ 0.22, from the first to the second PI.
An ANOVA was performed on these data with This effect was equivalent in both groups, since Group as a between subject factor and Condition there was no Group by PI interaction. In the simple (simple vs. choice), Direction (left or right button) RT condition, participants with PD were also and PI (1, 3, 5 s) as within subject factors. The slower to respond than control participants, results indicated that persons with PD were slower F(1, 22) ¼ 13.1, p < .01, 2 ¼ 0.37, and IT also than the control participants, F(1, 22) ¼ 14.6, decreased with PI from the first to the second PI, p < .001, 2 ¼ 0.40, and that IT decreased with PI, F(2, 44) ¼ 36.2, p < .001, 2 ¼ 0.62. However, a F(2, 44) ¼ 25.8, p < .001, 2 ¼ 0.54. Moreover, significant Group by PI interaction, F(2, 44) ¼ 3.3, the IT was longer overall in choice than in simple p < .05, 2 ¼ 0.13, indicated that the group differ- RT, F(1, 22) ¼ 59.7, p < .001, 2 ¼ 0.73. The ence varied with the PI. Although significant for all results also indicated a significant Condition by PIs, the group difference was larger on the first PI Direction interaction, F(1, 22) ¼ 5.1, p < .05, (1 s, p < .001, 2 ¼ 0.41; 3 s, p < .01, 2 ¼ 0.30; 2 ¼ 0.19. There was no significant RT difference 5 s, p < .01, 2 ¼ 0.33) The mean group differ- with response direction in the simple or the choice ence for each PI was 120, 84 and 94 ms,respectively, at 1, 3 and 5 s. Furthermore, therewas a larger PI effect for persons with PD(p < .001, 2 ¼ 0.58) than controls (p < .001, Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 2 ¼ 0.29). The RT improvement in simple RTfrom the 1 s to the 3 s PI was 73 ms in the PD groupand 37 ms in the control group.
Execution TimeAn ANOVA with Group as a between subject factorand Condition (simple vs. choice), Direction (leftor right button) and PI (1, 3, 5 s) as within subjectfactors was performed on the execution times. Thefindings indicated that participants with PD tooklonger to execute their responses than the controlparticipants, F(1, 22) ¼ 18.1, p < .001, 2 ¼ 0.45.
Fig. 1. Mean initiation time (ms) in simple and choice RT tasks as a function of preparatory inter-vals for PD (diamonds) and control (triangles) patients and 206 ms in control participants.
Moreover, in both groups, execution time was TEMPORAL PREPARATION AND RT IN PARKINSON’S DISEASE longer in the choice than the simple RT condition, In the alphabetic recall procedure, the capacity to F(1, 22) ¼ 16.8, p < .001, 2 ¼ 0.43. The mean manipulate information in working memory is execution time was 324 ms in simple RT and expressed by a performance score that reflects 393 ms in choice RT in the PD group and 182 the reduction in recall incurred by the alphabetical and 237 ms, respectively, in simple and choice RT condition (Direct recallÀAlphabetic recall/Direct in the control group. Importantly, no interaction recall). Based on the number of items recalled, with group was observed in execution time.
this score was 31% in PD patients and 16% innormal controls, which suggests that PD patients experienced greater difficulty recalling the words In general, participants made very few anticipa- in alphabetic order, t(22) ¼ 2.2, p < .05.
tions and errors and many of them made no errorsat all. The mean number of anticipations was, respectively for PD and control participants, 4 and 1.8 on the simple RT and 3.3 and 1.4 on the choice Correlational analyses were performed to assess RT. The mean number of incorrect responses on relations that might exist between performance on the choice RT task was 0.1 and 0.2 for PD RT tasks and factors known to affect RT perfor- participants and controls, respectively. Due to mance (e.g., chronological age, depression symp- the small number of errors and the frequent toms, motor symptoms). These results showed repetition of 0 scores among participants, non- interesting findings that should be interpreted cau- parametric (Mann–Whitney) tests were used to tiously given the small sample of participants.
assess group differences on global error scores.
Table 2 shows the results of these analyses. The The results indicated that there was no significant results indicated that for PD patients, there was no difference between PD patients and control par- significant relation between GDS score and perfor- ticipants on anticipatory responses and incorrect mance on the simple or choice RT task. Age was highly but not significantly related to initiationtime. Initiation time also shared a strong relation with performance on the psychomotor test (DSST)in both simple and choice RT, while execution time in these tasks was significantly related to the score The mean number of items completed in the on the motor test (Purdue Pegboard).
psychomotor test (DSST) was 39 in PD patients An important finding of the present study was and 49.5 in the control group. In the motor test that the PI had a larger impact on simple than (Purdue Pegboard), the mean number of items choice RT performance in persons with PD (i.e., completed was 14 in participants with PD and that PD patients do not prepare as much as controls Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 23.8 in controls. These results suggest a reduced for the shortest PI in simple relative to choice RT).
psychomotor and motor speed in PD patients, To express this effect, a specific preparation score although the group difference was significant for was derived to reflect the amount of preparation on motor speed only, t(22) ¼ À6.5, p < .001.
the shortest PI for choice over simple RT (Choice–Simple at 1 s)À(Choice–Simple at 3 s). With this formula, lower scores represent lower preparation at the shortest delay. Not surprisingly, the PD The mean number of digits recalled correctly was (À49.8) group had a significantly lower prepara- 7 in both the PD and control groups. Short-term tion score than controls (À15.2), t(22) ¼ À2.3, memory for words was also equivalent in both p < .05. We tested whether this preparation score groups, with a score of 4.4 in PD and 4.8 in was related to executive abilities as measured by controls. The visuo-spatial measure was the only the manipulation score from the alphabetic recall procedure. Moreover, we also assessed whether the t(22) ¼ À2.2, p < .05, although this difference preparation deficit was related to the capacity to was rather weak (4.4 in PD and 5.3 in controls).
maintain information in short-term memory as Table 2. Correlation Observed in PD Patients Between Performance on the RT Tasks (IT: Initiation Time, ET: Execution Time) and Age, Depressive Symptoms (GDS), Motor (Purdue) and Psychomotor Measures(DSST), and a Preparation Score.
Note. Alpha ¼ Direct recallÀAlphabetic/Direct recall, W-span ¼ word span, D-span ¼ digit span, VS ¼ visuo- spatial span, Preparation score ¼ (Choice–Simple at 1 s)À(Choice–Simple at 3 s), Dur ¼ duration of thedisease, Severity ¼ stage on the Hoehn & Yahr scale.
ÃSignificant at the .05 level (2-tailed).
ÃÃSignificant at the .01 level (2-tailed).
measured by standard verbal and spatial span tasks, enhance their performance with an increasing PI since Stuss et al. (1995) suggested that maintaining duration on simple and choice RT and that in both activation is an important aspect of preparation. As groups, the positive effect of PI is larger in simple shown in Table 2, there was no relation between RT than in choice RT. At first glance, the simila- manipulation of information and preparation in PD rities in performance and the equivalent group patients. However, a significant relation was found difference observed in simple and choice RT do between the preparation score and the ability to not readily support the hypothesis of a prepara- maintain information for a short time delay, as tory deficit in PD. However, preparation deficits assessed by word span, digit span and visuo-spatial are evident when considering the temporal param- span. It is worth noting that the preparation score eters of the tasks. Indeed, it was observed that the was unrelated to motor or cognitive speed, or to RT decrease from the first to the second PI in the clinical measures. In control participants, the simple RT condition was larger in the PD group relation was nonsignificant between the prepara- than in the control participants. This pattern of tion score and manipulation or span measures.
results was not obtained in the choice RT, in Finally, it can be argued that the pattern of RT which the PI effect was equivalent in both groups.
slowing and/or the preparatory deficit observed are As a result, the magnitude of the simple over related to severity or duration of the disease. To choice RT advantage was reduced in the shortest explore these issues, correlations were computed PI for PD participants. These results suggest that Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 between duration of the disease as measured by the deficit in the simple RT condition in PD years and the severity of the symptoms according to patients is dependent upon temporal parameters.
the stage of the Hoehn & Yahr scale. The results Notably, slowing was also observed in the choice (see Table 2) indicated that execution time (both in RT condition. This is consistent with findings simple and choice RT) was significantly related to from previous studies (Cooper et al., 1994; the Hoehn & Yahr scale, whereas initiation time Jahanshahi et al., 1992a) and could be due to and the preparation score did not correlate with this impairment or slowing in stimulus identification measure. Duration of the disease did not correlate and/or response selection processes. However, with any of the RT or preparation measures.
more importantly with regard to this study, thepattern of slowing in choice RT was independentof temporal factors. Taken together, these results bring support to the hypothesis that some aspectof preparing a specific voluntary action is The findings reported in the present study indicate impaired in PD and highlight the notion that that both PD patients and control participants temporal preparation interacts with specific TEMPORAL PREPARATION AND RT IN PARKINSON’S DISEASE preparation to account for the preparatory deficit deficits should have also occurred on choice RT.
Furthermore, Jahanshahi et al. (1992a) found no Before turning to a discussion of the theo- evidence of a general arousal deficit in PD retical implications of our findings, it is necessary patients when measuring the efficacy of warning to address some methodological issues that may signals on RTs. Second, PD patients may have relate to our finding that the specific preparation impairment in temporal processing of the whole deficit in PD participants is related to temporal temporal window in which PIs were embedded.
parameters. First, in the present study, partici- However, this is unlikely. Both groups showed an pants started the trial themselves. This was done equivalent PI effect in the choice condition, to ensure that participants were fully attentive suggesting that preparation, as a function of when the trial started with the PI occurrence.
increasing probability of signal, is a preserved Moreover, only three PI values varying over aspect of preparation in PD patients. Moreover, several seconds were used. This method may have there is no evidence in previous studies of a deficit enhanced the use of temporal cues. Thus, it is in temporal preparation per se in PD patients likely that using three PIs that varied over several (Jahanshahi et al., 1992a). Third, patients may be seconds favoured a large PI effect in the present slower in preparing a specific response. It is study, which allowed for the isolation of an effect indeed possible that persons with PD need a that was unexamined in previous studies.
longer minimal time to prepare a specific It can be argued that medication may affect the response. Although we cannot completely rule capacity of persons with PD to use temporal out this explanation, there are two indications that information in preparing motor responses, since lead us to some other explanations. First, previous all of our patients were on anti-parkinsonism studies have shown that PD patients do not take medication. However, this does not seem to be the longer to benefit from a warning cue in simple RT, case according to studies that have investigated even when cues are presented only 1 s prior to the this issue. Jahanshahi, Brown, and Marsden target (Bloxham et al., 1987; Jahanshahi et al., (1992b) found no impairment in the use of 1992a; Jordan et al., 1992; Rafal, Posner, Walker, temporal cues after withdrawal from dopaminer- & Friedrich, 1984). Second, there was no corre- gic medication. Independence of drug treatment lation between our preparation score and motor was also observed in Jordan, Sagar, and Cooper (1992), who compared treated and untreated PD A more satisfactory account of the preparatory patients on simple and choice RT and in Bloxham, deficit observed in PD in the simple RT task is that Dick, and Moore’s (1987) study, which investi- preparation of an action in a variable PI condition gated the detrimental effect of a dual task on depends on the probability of occurrence of the simple RT. It might also be argued that the pattern target across time. In a variable PI condition, the Downloaded By: [Canadian Research Knowledge Network] At: 15:46 3 June 2010 of results reported in this study is related to the subjective impression is that the shortest PI has severity of the disease. Comparability of the the lowest probability of occurrence. It is thus patients is in fact of major importance when possible that the larger group difference at the results from different RT studies are compared.
shortest PI comes from a different preparatory However, our results indicated that there was no strategy in PD. Patients may prepare their significant relation between severity or duration response for the most probable events to the of the disease and the preparatory deficit, detriment of the least probable events. Other although the severity of the disease was correlated studies have shown a larger RT deficit with greater stimulus uncertainty in PD, using other RT A number of explanations can be provided to paradigms (Brown et al., 1993; Cooper et al., account for the peculiar deficit of PD patients in the simple RT task, some of which can be ruled We argue that the strategy of favouring the most out by previous studies. First, PD patients may probable event arises from a difficulty maintaining need more time to achieve a general alertness the activation of a specific action schema for a state. However, if this were true, preparation large temporal window. When required to prepare an action in a variable temporal context, persons This work was supported by a FCAR (L.B.) and a with PD may favour the most probable moment FRSQ (L.B. and B.G.) Ph.D. fellowship, a FRSQ because this prevents them from maintaining the Chercheur-Boursier fellowship (S.B) and a grantfrom the MRC of Canada (S.B.). The authors wish to activation of action schemas over long periods.
thank Janet J. Boseovski for editing and helpful This interpretation is compatible with findings of a comments. This work was done as a partial fulfillment correlation in PD between specific preparation of a Ph.D. thesis by L.B. under the supervision of S.B.
(difference in simple and choice RT from the first in the Psychology Department of University of to the second PI) and performance on three classical retention measures (word span, digitspan and visuo-spatial span). This finding supports Stuss et al.’s (1995) proposal that preparing aresponse requires the activation and maintenance Belleville, S., Peretz, I., & Malenfant, D. (1996).
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