Slowing of Reaction Time in Parkinson|S Disease] the Involvement of the Frontal Lobes E[L[ Berryb\ \ R[I[ Nicolsonb\ J[K[ Fosterc\ M[ Behrmannd\ H[J[ Sagara

$Slowing of Reaction Time in Parkinson|S Disease] the Involvement of the Frontal Lobes E[L[ Berryb\ \ R[I[ Nicolsonb\ J[K[ Fosterc\ M[ Behrmannd\ H[J[ Sagara$

PERGAMON Neuropsychologia 26 "0888# 676Ð684

Slowing of reaction time in Parkinson|s disease] the involvement of the frontal lobes E[L[ Berryb\ \ R[I[ Nicolsonb\ J[K[ Fosterc\ M[ Behrmannd\ H[J[ Sagara

a Department of Clinical Neurolo`y\ University of Shef_eld\ Shef_eld\ UK b Department of Psycholo`y\ University of Shef_eld\ Shef_eld\ UK c Department of Psycholo`y\ University of Manchester\ Manchester\ UK d Department of Psycholo`y\ Carne`ie Mellon University\ Pittsbur`h\ PA\ USA

Received 10 May 0886^ accepted 08 October 0887

Abstract

This study investigated the possibility that the previously mixed _ndings relating to cognitive de_cits in Parkinson|s disease might be attributable to inhomogeneity within the patients sampled\ with attentional de_cits occurring only for those Parkinson|s patients who also have additional frontal lobe impairment[ Twenty!_ve patients with idiopathic Parkinson|s disease were classi_ed as showing frontal dysfunction\ or not\ on the basis of their performance on the Wisconsin Card Sorting Test and the picture arrangement subtest of the WAIS[ The two groups\ and a control group of normal elderly subjects matched for age and IQ\ undertook tests of visual attention designed to dissociate baseline response speed from central information processing speed[ Error rates did not di}er between the groups[ Performance of the non!frontally impaired Parkinson|s group was indistinguishable from that of the controls[ By contrast\ the {frontally impaired| Parkinson|s group responded signi_cantly more slowly than the controls[ Further analyses indicated that for the frontally!impaired Parkinson|s group\ information processing and automatic functions were unimpaired but there was a generalised slowing "as re~ected by increased baseline response time# which may represent a non!speci_c global cognitive impairment[ These _ndings suggest that the frontal lobes may be implicated in slowed response speed in Parkinson|s disease[ Þ 0888 Elsevier Science Ltd[ All rights reserved[

Keywords] Parkinson|s disease^ Cognitive impairment^ Attention^ Visual search

0[ Introduction Attentional control is believed to rely on the frontal lobes\ particularly the dorsolateral areas of the prefrontal Parkinson|s disease "PD# is primarily a disorder of cortex ð05\ 21Ł[ General lesions to the frontal regions can motor control[ However\ research over the last two dec! result in disorders of attention and arousal ð19\ 21Ł\ and ades has provided an extensive body of evidence associ! the connections between the prefrontal cortex and thala! ating frontal lobe type cognitive de_cits with the disease mus have frequently been implicated in arousal and aler! ð4\ 7\ 04\ 25\ 30\ 32Ł[ A number of authors have suggested ting functions\ sensory gating and directed\ selective and that loss of attentional control may underlie many of sustained attention "ð17\ 26\ 28Ł see Foster et al[ ð05Ł these cognitive de_cits ð5\ 6\ 09\ 00\ 23\ 27Ł[ For example\ for a review#[ A number of animal studies have also Brown et al[ ð5Ł suggested that the factor most associated demonstrated the role of the frontal lobes in attention with underlying cognitive dysfunction was a disturbance ð11\ 29\ 39Ł[ It is therefore particularly interesting that of a}ect:arousal[ On visual attention tasks\ Sharpe ð27Ł frontal lobe dysfunction is also associated with PD\ as found that patients with PD were more prone to inter! discussed below[ ference in the presence of distractor items than normal Traditionally\ dysfunction of the complex loop control subjects[ between the caudate nucleus and the prefrontal cortex resulting from striatal dopamine de_ciency is presumed Corresponding author[ Tel[] ¦33 9003 1115440^ fax] ¦33 9003 to underlie the cognitive de_cits of PD[ However\ 1655404^ e!mail] e[l[berryÝshe.eld[ac[uk depletion of dopamine in the mesocorticolimbic system

ð10Ł\ which also projects to the prefrontal cortex\ has led 1[ Method some investigators to suggest that it is the degeneration of this system that causes the observed de_cits ð12\ 14Ł[ 1[0[ Subjects Moreover\ there is dysfunction of non!dopaminergic neurotransmitter pathways innervating the frontal cortex Twenty!_ve right handed subjects with idiopathic PD in PD[ For example\ ascending cholinergic and nor! were recruited from the Movement Disorder clinic of the adrenergic projections to the frontal cortex are disrupted Royal Hallamshire Hospital\ She.eld\ U[K[ The group ð0\ 02Ł and altered levels of serotonin in the raphe nuclei consisted of 04 men and 09 women\ whose ages ranged have been related to depression and to cognitive de_cits from 31Ð66 years "mean age 48\ SD 09#[ All patients in PD ð15Ł[ Dysfunction of any one of these major neuro! ful_lled the diagnostic criteria of the PD Society\ namely] transmitter systems in subcortical!cortical pathways may akinesia with rigidity\ resting tremor or postural insta! alter cognitive behaviours that are mediated by the fron! bility\ and the absence of clinical signs of other causes of tal lobes ð24Ł[ Parkinsonism[ None of the subjects had a history of head To examine the changes in attentional function in PD injury\ alcohol abuse or other neurological disorder or and to determine the relationship between any de_cit and medical condition in which central function may become a de_cit involving the frontal lobes we employed two impaired other than PD[ tasks which permit dissociation between two di}erent The patients were allocated to one of two groups on aspects of attention] parallel "automatic# processing and the basis of their performance on the Wisconsin Card serial processing ð31Ł[ Treisman and Gelade used two Sorting Test "WCST#[ While the WCST is known to be tasks of visual attention[ In each task the subject has to sensitive to frontal lobe dysfunction ð08Ł there has been identify whether or not a target is present[ The task is some controversy surrounding the reliability of the complicated by the presence of a number of distractors[ WCST to measure frontal lobe impairment ð1\ 16Ł[ For In the {simple feature search| condition\ the target and instance\ Anderson et al[ ð1Ł argued that {the WCST can! distractors have no features in common "for example\ the not be interpreted in isolation as an indicator of frontal target may be a green T amongst brown Xs#[ Treisman lobe damage|[ However\ a recent PET study of normal found that in these circumstances the target appeared subjects has demonstrated that WCST performance is to {pop out| automatically\ being identi_ed rapidly and associated directly with enhanced activation of the dor! accurately regardless of the number of distractors[ In solateral prefrontal cortex[ In the context of PD\ Paolo the contrasting {conjoined feature search| condition\ the et al[ ð20Ł found that the WCST to be {sensitive to the target and distractors do share one feature "for example subtle executive de_cits demonstrated by persons with the target might be a green T amongst brown Ts and green Xs#[ In this latter condition the time taken to detect PD without dementia|[ the target typically increases linearly as the number of Performance on the WCST was scored according to distractors is increased[ Treisman and Gelade interpret the method of Heaton ð08Ł[ The {frontally impaired| the _ndings on conjunction in terms of their {feature group "PD!F# obtained three or fewer categories on the integration| theory of attention*the subject is required WCST and perseverated to the previous category[ In to serially search the stimuli in order to locate and identify order to increase the likelihood of frontal impairment\ it the target[ If there is a loss of attentional control as a is advisable to adopt a more stringent criterion\ namely result of a de_cit in cognitive processing\ reaction times increased perseverative errors on the WCST\ which is will increase disproportionately as the number of dis! claimed to be a relatively sensitive indicator of frontal tractors "display complexity# increases in the conjoined lobe dysfunction ð01\ 22Ł[ feature search condition[ The hypothesis which we are Consequently we can conclude that PD patients not advancing concerns the nature of the attentional de_cits showing de_cits on the WCST are not frontally impaired in PD and whether these impairments may be attributable and secondly that PD patients who show a de_cit on the to the existence of frontal dysfunction[ In order to test WCST are probably frontally impaired[ Subjects were this hypothesis we examined attentional function in two classi_ed as {frontally impaired| only if they performed groups\ one with frontal lobe impairment and one with! poorly on both number of categories achieved and num! out[ The hypothesis predicts that there should be a dis! ber of perseverative errors[ In addition\ the {frontally sociation\ with the {frontally impaired| PD group show! impaired| group exhibited impaired scores on The Wes! ing impaired performance on the visual search tasks "rela! chler Adult Intelligence Scale Picture Arrangement task tive both to the non!frontally impaired PD group and to "P ³ 9[90# ð33Ł\ thereby performing poorly on two tests the controls#\ whereas the non!frontally impaired PD which are sensitive "although not speci_c# to frontal lobe group should be unimpaired relative to the controls[ dysfunction[ Thus\ an aim of this study was to specify the precise The frontally impaired PD group consisted of 01 sub! nature of any attentional de_cits in PD\ while predicting jects^ 6 women and 4 men\ whose ages ranged from 32Ð that any impairment found will only arise in the patient 62 years "mean age 51[5\ SD 00[9#[ The second non! group who have additional frontal lobe dysfunction[ frontally impaired group "PD!NF# all produced _ve or E[L[ Berry et al[ : Neuropsycholo`ia 26 "0888# 676Ð684 678 more categories on the WCST and made no perseverative 2[ Materials errors[ This group contained 02 subjects comprising 2 women and 09 men\ with an age range of 31Ð66 years 2[0[ The experimental tasks "mean age 59\ SD 7[6#[ There were no signi_cant di}erences between the two Subjects completed two visual search tasks based on groups on tests of premorbid and current intelligence\ as those by Treisman and Gelade ð31Ł[ Subjects were measured by the National Adult Reading Test "NART# required to detect the presence of a target and to withhold ð18Ł "F"1\21# 0[481\ ns# and the Wechsler Adult Intel! the response on target absent trials[ The experiment com! ligence Scale Vocabulary Subtest respectively "WAIS prised two conditions^ simple feature search and con! Vocab# ð33Ł "F"0\12# 9[350\ ns#[ Both groups were joined feature search[ In each condition there were _ve administered the Beck Depression Inventory "BDI# ð2Ł blocks of 21 trials[ Half of each block of trials contained and the Blessed Dementia Scale "BDS# ð3Ł^ there were no target present trials and the remaining half were target signi_cant di}erences between the groups and no absent[ For both present and absent trials\ 9\ 2\ 5 or depression or dementia was found based on these scales 01 distractors appeared with equal probability[ Stimulus "F"0\12# 9[0[146\ ns#\ "F"0\12# 9[130\ ns#\ respec! presentation order within each block was randomised[ tively[ There was no signi_cant di}erence between the two On target present trials\ the target was equally likely to patient groups on three motor measures] Kings College appear in each quadrant of the screen[ All subjects were Rating Scale "KCRS# ð5Ł "F"0\12# 9[819\ ns#\ the motor tested on an Apple Macintosh computer[ In the simple score on the Uni_ed Parkinson|s Disease Rating Scale feature search condition\ the target di}ered from the dis! "UPDRS# ð03Ł "F"1\21# 0[481\ ns# and the Fine Finger tractors by only one feature[ The target was a small Movements test "FFM# ð8Ł "F"0\12# 9[1[537\ ns#\ in shaded circle[ The distractors were unshaded circles of which the subject is asked to rotate a spindle between the same size[ Target and distractors had a black outline[ thumb and fore_nger as quickly as possible for 29 s[ The In the conjoined feature search condition\ the target was groups did not di}er in the duration of the disease[ Mean the same as the simple feature search condition but the performance and SD on these tests are shown in Table 0[ distractors were either unshaded circles\ or shaded squa! Seventeen PD subjects were treated with a levodopa res[ Consequently the target was de_ned by a conjunction preparation "Madopar "04# Sinemet "1##\ four were taking of separate properties of the distractors "i[e[ the target dopamine agonists "bromocriptine "0#\ pergolide "1#\ lys! was uniquely speci_ed by the combination of being both uride "0## and two subjects were on an anticholinergic shaded and a circle#[ For all subjects the simple feature preparation "benzhexol#[ Two of the patients were un! search task was administered _rst[ treated[ A control group of age matched healthy subjects "Con! trols# was drawn from members of Age Concern in 3[ Procedure She.eld\ U[K[ There were 09 subjects\ 7 female and 1 male\ whose ages ranged from 41Ð58 years "mean Subjects had been preselected on the basis of their age 51[5\ SD 4[91#[ None of the subjects performed psychometric test performance\ taken within the previous abnormally on the Blessed Dementia Scale "mean 1\ six months prior to this experiment as part of a longi! SD 1#[ NART score for this group was not signi_cantly tudinal study within the department "Table 0#[ Subjects di}erent from either of the two PD groups were asked to sit directly in front of the computer at a "mean 002[3\ SD 8# "F"1\21# 9[420\ ns#[ distance that was comfortable to them[ They were told

Table 0 Performance of the two groups on criterion and psychometric tests

WCST WAIS P[A[ NART BDS WAIS BDI KCRS UPDRS Duration Vocab[ Categories Perseveration

Frontal 0[9 29[2 5[64 009[2 1[14 01[43 7[05 08[9 12[9 3[0 "5[5# "1# "09# "1# "1[4# "3# "01[4# "02# "0[72# Non!frontal 7[14 00[3 8[35 098[4 1[34 02[96 09[50 04[9 04[9 3[1 "4[0# "2# "8# "2# "1[4# "5# "6[9# "7[9# "0[3#

WCST\ Wisconsin Card Sorting Test^ WAIS P[A[\ Weschler Adult Intelligence Scale "Picture Arrangement#^ NART\ National Adult Reading Test^ BDS\ Blessed Dementia Scale^ WAIS Vocab\ Weschler Adult Intelligence Scale "Vocabulary Test#^ BDI\ Beck Depression Inventory^ KCRS\ Kings College Rating Scale^ UPDRS\ Uni_ed Parkinson|s Disease Rating Scale[ 689 E[L[ Berry et al[ : Neuropsycholo`ia 26 "0888# 676Ð684 to rest their right hand lightly on the space bar of the computer keyboard[ Subjects were instructed to respond only when they detected the target and to do so as quickly as possible[ They were then given a practice run of four trials during which time further explanation was provided when necessary[ No explicit feedback was given\ but the score was shown in the bottom right hand corner of the screen during the testing phase[ This score showed two _gures^ one which gave the number of trials presented\ and another which showed the number of correct responses[ Errors could be either omissions or commissions[ Subjects took short breaks between blocks[ The test session took approximately 34 min[ Fig[ 1[ Example screen display for the conjoined feature search condition[

4[ Results

4[0[ Errors of omission and commission

No omission errors were made by any of the subjects[ In addition\ no more than two errors of commission were made by any subject and the mean error rates did not di}er signi_cantly between groups "F"1\026# 1[95\ ns#[

4[1[ Reaction times

It may be seen from Figs 2 and 3 that the pattern of results in both conditions is as Treisman predicted[ There was no increase in reaction times as the numbers of dis! tractors increased in the simple feature search condition\ whereas in the conjoined feature search condition the reaction times increased proportionally as the number of alternatives increased[ Interestingly\ this normal pattern of results occurs for all three subject groups[ The pattern of reaction time performance across trials was analysed using a 1!Factor analysis of variance of group "PD!F\ Fig[ 2[ Latencies for the simple feature search condition[ Mean reaction times and standard deviation for each of the three subject groups with PD!NF\ Controls# by condition "simple feature search\ 9\ 2\ 5 and 01 distractors appearing with the target[ In this condition conjoined feature search#[ The analysis showed sig! reaction times do not increase as the number of distractors increase[ ni_cant main e}ects of group and condition "F"1\21# 5[1\ P ³ 9[90^ F"0\21# 245[4\ P ³ 9[9990 respectively# and a signi_cant interaction between group and condition "F"1\21# 2[53\ P ³ 9[94#[ Graph means indicated that the interaction between group and con! dition was due to an increase in the reaction time of the control subjects on the 01 array size only in the simple feature search\ relative to the two patient groups[ The reaction times of the control group fell between the two patient groups in this condition[ Post hoc analysis indi! cated that the PD!F group had signi_cantly slower reac! tion times on both conditions than either the PD!NF group or the controls "P ³ 9[90#[ There was no signi_cant di}erence between the PD!NF group and the controls "P × 9[94#[ For all the subject groups\ the conjoined fea! ture search condition produced signi_cantly slower reac! tion times overall than the simple feature search condition "P ³ 9[990#[ Fig[ 0[ Example screen display for the simple feature search condition[ A 0!Factor analysis of variance of group means "PD! E[L[ Berry et al[ : Neuropsycholo`ia 26 "0888# 676Ð684 680

or the intercept or both[0 A greater slope would suggest a reduced rate of information processing "an e}ect of executive control#\ while a higher intercept would indicate a general psychomotor slowing independent of complexity\ possibly implicating a general de_cit in arou! sal:vigilance[ An analysis of variance was then performed on the intercept and slope separately[ Mean values for slope and intercept for each experimental condition are given in Table 1[

4[3[ Results for the intercept

An overall 1!Factor Analysis of Variance of group "PD!F\ PD!NF\ Controls# and condition "simple feature search\ conjoined feature search#\ was undertaken[ There was a signi_cant e}ect of group "F"1\21# 2[1\ P ³ 9[94#[ The PD!F group were slower than either the PD!NF group or the Controls[ There was no signi_cant e}ect of Fig[ 3[ Latencies for the conjoined feature search condition[ Mean condition "F"0\21# 2[3\ ns# or of group by condition reaction times and standard deviation for each of the three subject "F"1\21# 9[21\ ns#[ Further analyses using a 0 Factor groups with 9\ 2\ 5 and 01 distractors appearing with the target[ The Analysis of Variance of group "PD!F\ PD!NF\ Controls# greater the number of distractors\ the slower the reaction time as the subject serially searches the screen[ separately for each condition revealed a highly signi_cant e}ect of group on the conjoined feature search condition "F"1\21# 5[4\ P ³ 9[90#[ The PD!NF and the control subjects sustained faster reaction times than the PD!F group in this condition[ There was no signi_cant e}ect of F\ PD!NF\ controls# was carried out for each condition group in the simple feature search condition separately[ "F"1\21# 0[49\ ns#[ In the simple feature search condition there was a In a further analysis\ an overall 1!Factor Analysis of signi_cant e}ect of group "F"1\21# 3[79\ P ³ 9[94#[ The Variance of group "PD!F\ PD!NF# and condition "simple PD!F group had signi_cantly slower reaction times than feature search\ conjoined feature search#\ was carried out the PD!NF group\ or the Controls "F"0\12# 6[30\ on the PD groups alone[ Results revealed a signi_cant P ³ 9[94^ F"0\19# 3[85\ P ³ 9[94^ respectively#[ There e}ect of group and of condition "F"0\12# 5[7\ P ³ 9[94^ was no signi_cant di}erence in reaction times between F"0\12# 24[11\ P ³ 9[990 respectively#[ The PD!NF the PD!NF and the Control group "F"0\10# 9[158\ ns#[ showed faster reaction times than the PD!F group[ For In the conjoined feature search condition there was a both groups\ the conjoined feature search produced signi_cant e}ect of group "F"1\21# 5[48\ P ³ 9[90#[ As slower reaction times overall than the simple feature in the previous condition\ the PD!F group showed sig! search condition[ Again\ there was no signi_cant inter! ni_cantly slower reaction times than the PD!NF group action between group and condition "F"0\12# 9[90\ ns#[ "F"0\12# 6[56[ P ³ 9[94Ł and the Control group Closer analysis of main e}ects revealed a signi_cant e}ect "F"0\19# 09[77\ P ³ 9[90#[ Again\ there was no sig! of group on both the simple "F"0\12# 5[5\ P ³ 9[94# and ni_cant di}erence between the PD!NF group and the conjoined "F"0\12# 5[0\ P ³ 9[94# condition[ In both Controls "F"0\10# 9[903\ ns#[ conditions\ the PD!NF subjects produced faster reaction times than the PD!F group[ Inspection of the data for 4[2[ Intercept and Slope the simple feature search condition indicated that the

It may be seen from Figs 2 and 3 that the data for all 0 groups follow the expected pattern[ In the simple feature Unfortunately\ slope and intercept co!vary\ and therefore in order to analyse the performance for slope and intercept separately\ the cen! search condition there is little or no change in latency as troid of each individual|s four data points was calculated[ The centroid the number of distractors increases\ whereas there is the is the most reliable summary statistic for the overall data\ and the expected linear increase in latency with number of dis! regression line will always travel through it[ Independent estimates of tractors in the conjoined feature search condition[ It is intercept and slope may be obtained by evaluating the intercept by therefore appropriate to perform a linear regression on projecting backwards a line from the individual centroid with slope equal to population mean\ and second calculating the slope of the line the data^ a procedure which determines the intercept and from the individual|s centroid to the population mean intercept[ These the slope of the best _t straight line through the four represent the most robust\ unbiased estimates for the intercept and points[ It is quite possible that PD may a}ect the slope slope respectively[ 681 E[L[ Berry et al[ : Neuropsycholo`ia 26 "0888# 676Ð684

Table 1 Mean and SD for the intercept and slope

Simple feature search Conjoined feature search

Intercept "s# Slope Intercept "s# Slope "s:distractor# "s:distractor#

Frontal 9[447 −9[990 9[50 9[911 "9[093# "9[994# "9[98# "9[90# Non!frontal 9[375 9 9[430 9[91 "9[951# "9[991# "9[981# "9[994# Controls 9[495 9[991 9[417 9[910 "9[935# "9[995# "9[068# "9[995#

reason for the discrepancy between the two!group data 5[ Discussion here and the three!group data above was that the control group performance lay between the two PD groups "for The results of the visual search tasks produced three the 01 array size only#[ main _ndings[ First\ in the simple feature search Finally\ a 1!Factor Analysis of Variance was carried condition\ the reaction times of both the PD groups and out on the PD!NF and Controls group alone[ There was the control group remained at a constant level regardless no signi_cant di}erence between the groups\ or con! of the number of distractors presented\ indicating that ditions "F"0\10# 9[09\ ns^ F"0\10# 9[24\ ns respec! their parallel processing was intact "and that the target tively#[ There was no interaction between group and did indeed {pop out| as Treisman and Gelade predict#^ condition "F"0\10# 1[00\ ns#[ second\ in the conjoined feature search condition there were no di}erences between the groups in the e}ects of task complexity "slope of the regression line#[ This 4[4[ Results for the slope indicates that there was no information processing de_cit in PD due to an increase in cognitive complexity on this An overall 1!Factor Analysis of Variance of group task[ Third\ baseline speed of response "the intercept# was "PD!F\ PD!NF\ Controls# and condition "simple feature signi_cantly slower in both conditions for the {frontally search\ conjoined feature search# indicated that there was impaired| group but not for the non!frontally impaired no overall signi_cant e}ect of group "F"1\20# 0[99\ ns#[ group compared with controls[ Before interpreting these There was a highly signi_cant e}ect of condition _ndings\ however\ it is important to assess the extent "F"0\20# 047[23\ P ³ 9[9990#[ It appears that for all to which the reduced baseline response speed might be groups\ slopes were signi_cantly higher on the conjoined attributable to motor output limitations speci_c to the feature search condition[ There was no interaction {frontally impaired| PD group[ between group and condition "F"1\21# 0[29\ ns#[ If poor performance is related to bradykinesia then In a further analysis\ an overall 1!Factor Analysis of there should be a positive correlation between motor Variance of group "PD!F\ PD!NF# and condition "simple ratings and reaction times[ A correlation analysis was feature search\ conjoined feature search#\ was carried out undertaken to assess this possibility[ There was no sig! on the PD groups alone[ Results revealed no signi_cant ni_cant di}erence between the {frontally impaired| and e}ect of group "F"0\12# 0[01\ ns# but a highly signi_cant non!frontally impaired PD groups in their motor ratings e}ect of condition "F"0\10# 094[71\ P ³ 9[9990#[ For "F"0\19# 2[72\ ns#\ and for both groups only a small both groups\ slopes were signi_cantly higher on the con! non!signi_cant correlation between these ratings and joined feature search condition[ There was no interaction reaction times on the task "r 9[19#[ However there was between group and condition "F"0\12# 1[16\ ns#[ a signi_cant correlation "r 9[29# between _ne _nger Finally\ a 1!Factor Analysis of Variance was carried movement "FFM# scores and baseline reaction times on out on the PD!NF and Controls group alone[ There was this task for both PD groups[ Nonetheless\ the non!front! no signi_cant e}ect of group but a highly signi_cant e}ect ally impaired group\ who are by de_nition motor!im! of condition[ "F"0\19# 0[837\ ns^ F"0\19# 191[84\ paired "and to the same degree as the {frontally impaired| P ³ 9[9990#[ Again\ for both groups\ slopes were sig! group#\ produced reaction times that were no slower than ni_cantly higher on the conjoined feature search those of the control subjects who have no motor dysfunc! condition[ There was no interaction between group and tion[ This is critical\ because it suggests that the type of condition "F"0\19# 9[23\ ns#[ motor disability characterised by PD does not sig! E[L[ Berry et al[ : Neuropsycholo`ia 26 "0888# 676Ð684 682 ni_cantly impair the ability to carry out this task[ out the task are no di}erent from the controls in this However\ since there was a correlation between FFM group[ The angle of the slope on the conjoined feature scores and baseline reaction times for both PD groups task did not increase disproportionally as the number we explored the possibility of defective motor control of distractors increased in this frontally impaired group further by taking into account the speci_c nature of the which suggests that the de_cit observed is independent of movement required to complete the task e}ectively[ The the processes that require selective attention[ This result experimental task undertaken involved the single is compatible with that of previous studies examining depression of a _nger in order to move the space bar[ PD populations[ The intercept\ which is a reaction time This movement is similar to the {Finger Taps| rating on corresponding to the detection of a target with no alter! the UPDRS and KCRS\ and for this reason\ the _nger natives "distractors#\ is equivalent to a simple reaction taps scores for each PD subject was analysed separately[ time paradigm[ As such\ our results gain direct support There was no signi_cant di}erence between the groups on from research undertaken by Jordan et al[ ð13Ł[ In this this single score\ nor did the ratings correlate signi_cantly study\ a group of PD patients and control subjects were with reaction times "r 9[0#[ Finally\ an analysis of examined on simple reaction time "SRT# in which subjects covariance was undertaken for all of the subject groups\ consistently respond in the same way regardless of the with the _nger taps as the covariate[ This analysis still stimulus^ and on go:no!go choice reaction time "CRT#\ resulted in a signi_cant di}erence between groups on the where the response is di}erent depending upon the nature intercept "F"0\10# 7[9\ P ³ 9[90\ F"0\10# 3[4\ of the stimulus[ Results revealed a prolongation of SRT P ³ 9[94^ simple feature search and conjoined feature which correlated with the number of perseverative search respectively#[ Overall\ therefore\ there was no sig! responses on the Wisconsin Card Sorting Test[ The ni_cant di}erence between the two PD groups in motor authors suggest that these results indicate that frontal ratings\ and no correlation between motor ratings in the lobe function may be a critical in~uence in the genesis of two PD groups and experimental results on the intercept slowed response speed in PD[ In an interesting study by or slope for either condition[ We can conclude therefore Goodrich et al[ ð07Ł\ control subjects were relatively more that the baseline di}erences in speed between the two impaired than a PD group on an SRT task by the impo! Parkinson|s groups are not caused directly by motor skill sition of a secondary oral reading task\ e}ectively abol! de_cits[ ishing the usual SRT de_cit attributed to PD patients[ The performance of the non!frontally impaired group Goodrich et al[ propose that their results can be attri! was equivalent to that of the control subjects[ By contrast\ buted to evidence of an attentional demanding process the baseline performance of the {frontally impaired| that confers speed on the control group|s SRT\ but which group was impaired relative to the other two groups\ cannot be utilised under dual task conditions[ Par! though on the conjoined feature task the increase in reac! ticularly pertinent to our research was the suggestion that tion time as the number of targets increased was normal[ in PD there is an impairment in this attention demanding In other words\ taken as a group\ the {frontally impaired| process which does not allow them to use it under normal patients were not disproportionally slowed compared to SRT conditions[ the non!frontally impaired PD group as the array size In summary\ the PD group who had no frontal impair! increased[ Therefore\ while no central processing de_cit ment performed as well as the controls on all aspects appears to exist\ the patients exhibit a constant slowing of the visual search tasks[ The PD group with frontal of response speed in an otherwise intact performance[ dysfunction showed signi_cant slowing of global baseline The impairment is simple\ absolute and independent of response speed "but no di}erential slowing as a function the cognitive complexity of the task and may represent a of number of distractors#[ The data are consistent with non!speci_c global impairment[ There are strong grounds the hypothesis that cognitive dysfunction a}ecting to believe that the {frontally impaired| patients do indeed response speed may ensue only for a subgroup of PD su}er from frontal dysfunction\ as re~ected by their poor patients for whom the pathophysiology also a}ects the performance on the WCST generally and speci_cally on frontal lobes[ perseverative errors "see Method for a fuller discussion#[ The results therefore suggest that the frontal lobes may be critical in slowed response latencies in Parkinson|s disease[ Acknowledgements The results of this study are consistent with our pre! diction that impairment on this task would only ensue We are very grateful to Peter Co}ey and Donald Stuss for the {frontally impaired| group\ thus implicating the for facilitating the work reported in this article[ We would frontal lobes in the pathology of cognitive dysfunction also like to acknowledge grant support to Marlene in PD[ However\ according to Treisman|s theory\ the Berhmann from the National Institute of Mental Health impairment is not one of attention per se\ since the MH43135 and to Jonathan Foster through a NATO e.ciency of central cognitive processes required to carry Collaborative Science Grant "CRG!839056#[ 683 E[L[ Berry et al[ : Neuropsycholo`ia 26 "0888# 676Ð684

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