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Psychomusicology, lly 96-118 ©1992 Psychomusicology

P3 EVENT-RELATED POTENTIALS AND PERFORMANCE OF HEALTHY OLDER AND ALZHEIMER'S DEMENTIA SUBJECTS FOR MUSIC PERCEPTION TASKS Kenneth P. Swartz Joseph P. Walton University of Rochester Medical Center Garry C. Crummer Edwin C. Hantz Eastman School of Music Robert D. Frisina University of Rochester Medical Center Event-related potentials and performance responses were recorded from healthy older subjects and from subjects with Senile Dementia of the Alzheimer's Type (SDAT) performing six tasks involving auditory discrimination of music stimuli. Tasks included pure tone, timbre, rhythm and interval discrimination, detection of a meter shift, and discrimination of open and closed harmonic endings for chord progressions. Mean P3 latency was longer and performance was poorer for SDAT subjects, but they displayed surprising vigilance and mostly above-chance performance. SDAT subjects had a tendency not found for healthy subjects to produce false alarms on the more difficult tasks. Some SDAT subjects produced clear P3 potentials despite chance level performance. The P3 may thus provide a useful measure of neural and cognitive responses to music despite impaired response processing or confusion in SDAT subjects. Despite severe impairment of memory, language, and several other cognitive functions, persons with Alzheimer's disease (Senile Dementia of the Alzheimer's Type or SDAT) seem to respond to music with remarkable attention and comprehension (Katzman, 1986; Swartz, Hantz, Crummer, Walton, & Frisina, 1989). Several authors of the present report have become aware of this response, both by observations of patients with Alzheimer's disease undergoing music therapy, and by conversations with caregivers and music therapists. In several instances, we have observed patients who engage in music activities in an apparently normal manner, singing songs, dancing, and exercising in synchrony with music. The same patients, however, were apparently unable to produce or fully comprehend normal conversation or to remember that they had recently met a particular individual. In general, responses of Alzheimer's patients to music include body movements and dancing in synchrony with the music, singing, increased socialization, decreased agitation, and overall improvement of mood. Additional reports of the benefits of providing music stimulation to demented patients are given in the literature (Bower, 1967; Charatan, 1980; Clark & Witte, 1991), including for patients in the later stages of Alzheimer's disease (Katzman, 1986; Norberg, Melin, & Asplund, 1986). 96

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In this context there is clear motivation for systematic experimental investigations of the neurophysiological and cognitive psychological responses of Alzheimer's patients to different aspects of music. Such systematic study can provide detailed knowledge of the specific aspects or elements of music which induce corresponding specific positive responses of Alzheimer's patients to music. These details could, in turn, contribute to the improvement of music therapies for Alzheimer's patients. Furthermore, such studies may also provide clues to some aspects of the fundamental nature of music processing. If, for example, we can demonstrate intact cognition of harmonic closure in Alzheimer's disease, this would imply that such cognition does not crucially rely on processes such as short term memory or semantic processing which are severely impaired in Alzheimer's disease. Similar implications would hold for other music cognitive processes, providing clues to how the preservation or impairment of such cognitive processes relate to the cognitive processes known to be affected by Alzheimer's disease. Our motivation for studying neurophysiological as well as behavioral responses to music in Alzheimer's disease stems from the fact that although conventional tests of music perception and understanding (Boyle & Radocy, 1987; Sloboda, 1985) can be of some help in assessing the Alzheimer's patient's response to music, they have serious shortcomings because they rely heavily on verbal instructions which Alzheimer's patients find difficult to comprehend. Consequently, our study employs a measure which is independent of the subject's behavioral response. This measure is the event-related potential (ERP) which we will now explain in some detail. ERPs are measures of voltage changes on the scalp elicited by sensory events. A common experimental paradigm (used here) for eliciting ERPs is the so called "oddball" paradigm. In this paradigm the subject hears a sequence of discrete sounds each of which belongs to one of two categories, a "standard" sound or a "target" sound. The sequence of standards and targets is typically random, and the target sound occurs less frequently than the standard sound. Consequently, the target sound is also called the "oddball." The subject's task is to respond to the target sound. The resulting ERP typically varies between positive and negative voltage changes. The third positive voltage peak that occurs on average after the subject hears the oddball is called the "P3" or "P3 component of the ERP" and has been widely studied (Hilly ard & Picton, 1987; Regan, 1989). The P3 is typically characterized by two parameters, its amplitude and latency. The P3 amplitude is the height of the voltage peak (in microvolts), referenced to the average voltage level recorded prior to when the subject hears the target sound. The P3 latency is the time (in milliseconds) from the onset of the target sound to the occurrence of the P3 voltage peak. P3 amplitudes are typically on the order of 10 microvolts and the latency is typically on the order of several hundred milliseconds. Because the P3 results from the synchronous electrical activity of large groups of nerve cells, the P3 amplitude and latency can be loosely interpreted as measures of the strength and speed of neural processing involved in the task that elicits the ERP. Swartz, Walton, Crummer, Hantz, and Frisina

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In the experimental history of P3 measurements the amplitude and latency have been found to correlate with many manipulable psychological variables. The P3 amplitude tends to increase with such factors as the significance of the target, the rarity of the target, and target salience. P3 latency tends to decrease as target/standard discriminability increases, or for increased attentional state or cognitive ability of the subject. In general, these correlations are often summarized by concluding that the P3 amplitude and latency are sensitive to the psychological properties of subjective significance and subjective probability (Donchin, Karis, Bashore, Coles, & Gratton, 1986; Hillyard & Picton, 1987; Regan, 1989). Thus, amplitude increases and latency decreases as the significance or meaning of the target to the subject increases, and also as the target occurs less frequently or becomes more surprising in other manipulable ways such as the breaking of established auditory sequential patterns. The P3 is consequently a seemingly apt measure for the study of music perception and cognition since the psychological factors of subjective significance and subjective probability are fundamental factors in music cognition. Thus, individual pitches, chords, timbres, and rhythmic, melodic, dynamic (sound intensity), and textural (combinations of different auditory streams often each associated with its own timbre) patterns are all manipulated in music compositions to have varying degrees of stability. These music elements fulfill the listener's expectations to varying degrees and also have varying amounts of significance for the listener. Several investigations have, in fact, already demonstrated the usefulness of the P3 component of the ERP in studying differences in the neural processing of music as a function of music training and special music listening abilities such as absolute pitch (Chuang, Frisina, Crummer, & Walton, 1988; Crummer, Hantz, Chuang, Walton, & Frisina, 1988; Frisina, Walton, & Crummer, 1988; Hantz & Crummer, 1988; Hantz, Crummer, Wayman, Walton, & Frisina, 1992; Walton, Frisina, Swartz, Hantz, & Crummer, 1988; Wayman, Frisina, Walton, Hantz, & Crummer, 1992). In terms of cognition, the P3 is widely hypothesized to be a neurophysiological index of cognitive processing of stimuli (discrimination, categorization, and evaluation), involving aspects of primary or short-term memory (cognitive closure, updating of working memory, resolution of expectancy or uncertainty) (Donchin et al., 1986; Regan, 1989). Such short-term memory and learning related functions for nonmusic tasks are profoundly impaired by SDAT (Kaszniak, 1986; Katzman, 1986). Consequently, the P3 is also an apt probe of SDAT subjects' responses to music stimuli. The P3 component of the ERP is further likely to be sensitive to the effects of SDAT, both because of the regions of the brain and the psychological functions most severely affected by the disease. While the neural generators of the P3 are not known with complete certainty, evidence suggests that the amygdala, hippocampus, and parietal cortex are all involved in P3 generation, at least for some tasks (Halgren, et al., 1980; Kiss, Dashieff, & Lordeon, 1989; Marsh, et al., 1990). These regions are among the most severely affected in SDAT by cell loss and by the presence of neuritic plaques and neurofibrillary tangles (Karp & Mirra, 1989; Katzman, 1986). Furthermore, Marsh (1990) and colleagues found 98

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a significant inverse correlation between glucose metabolism in the parietal association area, as measured by positron emission tomography, and P3 latency in early stage Alzheimer's patients. SDAT would thus be expected to significantly degrade the P3, though the degree of the effect may well depend on the task (e.g., musical as opposed to nonmusical) which may alter the regions of neural activity that contribute to the potential (Halgren, 1988). Numerous studies of the P3 component of the ERP in demented subjects have been published. These experiments have generally employed simple auditory or visual oddball paradigms and have focused on three areas. First, they have been concerned with finding differences in P3 measures between patients with Alzheimer's dementia (grouped in some studies with patients who had dementias of other etiologies) as compared to healthy age-matched controls (Goodin, Squires, & Starr, 1978; Gordon, Kraiuhin, Harris, Meares, & Howson, 1986; Pfefferbaum, Wenegrat, Ford, Roth, & Kopell, 1984). Second, studies have examined differences in P3 measures between subjects with Alzheimer's dementia and patients with depression, schizophrenia, multi-infarct dementia, Korsakoff s syndrome and some other illnesses (Blackwood, St. Clair, Blackburn, & Tyrer, 1987; Gordon et al., 1986; Pfefferbaum, Wenegrat, Ford, Roth, & Kopell,1984; Slaets & Fortgens, 1984). Third, several studies have examined P3 measures as a function of the progression of Alzheimer's disease, using both longitudinal and cross-sectional designs (Ball, Marsh, Schubarth, Brown, & Strandburg, 1989; Goodin, Starr, Chippendale, & Squires, 1983; Polich, Ehlers, Otis, Mandell, & Bloom, 1986; St. Clair, Blackburn, Blackwood, & Tyrer, 1988). Generally, Alzheimer's patients, as well as demented patients of mixed etiologies, have been found to have significantly longer P3 latencies than do healthy age-matched subjects (Goodin et al., 1978; Michalewski, Rosenberg, & Starr, 1986; Regan, 1989) including for early stage Alzheimer's dementia subjects (Polich, Ladish, & Bloom, 1990). Other studies, however, have found either no effect or a less significant effect, presumably due to differences in task, subject selection and ERP evaluation (Pfefferbaum, Wenegrat, Ford, Roth, & Kopell, 1984; Slaets & Fortgens, 1984). Comparing dementia to non-dementing brain disorders, significant P3 latency differences have sometimes been found (Goodin et al., 1978; Gordon et al., 1986) and sometimes not (Pfefferbaum, Wenegrat, Ford, Roth, & Kopell, 1984; Polich et aL, 1986). Again, this discrepancy may be explained, as Pfefferbaum, Wenegrat, Ford, Roth, & Kopell,(1984) note, by "... a number of differences in the paradigms, the analysis techniques and also in the patient and control samples," all of which are explained in detail in their paper. Several authors have reported a positive correlation between P3 latency and cognitive decline indicated by specific assessments such as the Mini-Mental State Exam (Blackwood et al., 1987; Folstein, Folstein, & McHugh, 1975; Lai, Brown, Marsh, & LaRue, 1983; Polich et al., 1986) or by the longevity of the dementia (Ballet al., 1989; Goodin etal., 1983; St. Clair etal., 1988). Significant differences in P3 amplitude have not been commonly reported.

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In this paper we report on initial experiments using the P3 component of the ERP to measure the perception and information processing of music stimuli by subjects with SDAT. We compare the behavioral and neurophysiological SDAT responses to those of healthy age-matched controls. Since ERPs are elicited by repeated responses to music stimuli of the same type, the ERP measure is best suited to the study of cognitive "building blocks" of music such as isolated intervals or short chord sequences. Consequently, six different tasks were utilized involving the perception and discrimination of pitch, timbre, melodic interval, chord sequences, rhythmic patterns, and meter. An important result of this study is that both behavioral and neurophysiological measures suggested that SDAT subjects were able to successfully perform and understand these music tasks. Furthermore, the P3 was found to offer promise as a neurophysiological index of information processing for SDAT subjects who are confused by or somehow unable to make conventional, overt motor responses to specific music tasks (Polich, 1987; Swartz et al., 1989). Methods Subjects Twelve healthy subjects were recruited from the local community. These subjects ranged in age from 65 to 85 years old with a mean age of 73. Seven of these subjects were female and five were male. All of these subjects were screened by questionnaire to ensure that they had no major medical disorder that produced significant cognitive impairment, and no history of brain disease, head trauma, major psychiatric problems, or alcohol or drug-dependency. Subjects were also required (again by self-report) to hear well enough that they could conduct a normal conversation without the use of a hearing aid. Subjects with Alzheimer's disease were recruited from local nursing homes and from a memory disorders clinic at a local hospital. The resulting group consisted of six subjects ranging in age from 69 to 78 years old with a mean age of 76. Two of these subjects were female and four were male. Alzheimer's subjects were screened in two ways. First, medical charts were reviewed to ensure that subjects had no source of cognitive impairment other than SDAT, including other major medical disorders known to cause cognitive impairment, head trauma, or a history of psychiatric illness, or alcohol or drug dependency. Subjects with a history of hearing impairment were also excluded. Charts were also reviewed to verify that subjects satisfied the NINCDS-ADRDA (National Institute of Neurological and Communicative Disorders - Alzheimer's Disease and Related Disorders Association) criteria for the diagnosis of probable Alzheimer's disease (McKhann, et al., 1984). To obtain these subjects, over one hundred charts were reviewed with the assistance of a consulting geriatrician, a consulting neurologist, and an otolaryngology senior resident. The Mini-Mental State Exam (Folstein et al., 1975) scores for the SDAT subjects ranged from 8 to 27 (out of a possible 30) with a mean of 20. The second screening procedure used for the SDAT group was a music pretest administered in each subject's home. (Ten subjects were given this test.) Representative parts of five of the stimulus series and one full series 100

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(Timbre) were played over headphones, and the subject was asked to identify the target by signaling with his hand. This ensured that SDAT subjects were comfortable with the tasks and able to perform most of them adequately with the vigilance required for testing in the laboratory. The inherently poor memory of SDAT subjects for newly learned material (the time between the pretest and the first laboratory test was at least several days) and the absence of any day effects (i.e., there were no statistically significant differences between the results of testing subjects on the two different days on which they were tested) in the laboratory data both indicate that pretesting did not introduce any training effects. Although none of the SDAT subjects had received formal music training in a music degree program, it was not possible to reliably assess the amount of experience they had in playing music instruments. Stimuli and Procedures Subjects were tested on two different days, both times on all of six different stimulus series: Pure Tone, Timbre, Interval, Rhythm, Chord, and Meter. All subjects were tested on all series except for the Meter series, for which eight healthy and five SDAT subjects were tested. The Meter series was dropped part way through our study in order to make the length of testing sessions more comfortable for the subjects. The standard and target stimuli for the more complex series are presented in music notation in Figure 1. The most important quantitative features of the series are given in Table 1. In the TIMING column, DUR indicates the total duration of each target or standard stimulus (for example, the duration of the three notes comprising the Rhythm series target or standard is 800 ms). In the same column, ISI indicates the interstimulus interval, the time from the end of each target or standard to the beginning of the next. Table 1 Description and Timing Characteristics of Music and Pure Tone Stimuli SERIES DESCRIPTION TIMING EPOCH PRESTIMULUS Pure Tone Standard: 0.5 kHz DUR: 333 ms 1500 167 ms Target: 1.0 kHz ISI: 2.67 s ms Timbre Standard: Viola DUR: 333 ms 1500 167 ms Target: Tuba ISI: 2.67 s ms Interval Standard: Maj 2nd DUR: 1 s 2000 250 ms Target: Maj 7th ISI: 4 s ms Chord Standard: Open Series DUR: 3.5 s 4500 250 ms Target: Closed Series ISI: 8 s ms Rhythm Standard: 216ths-8th DUR: 800 ms 1800 200 ms Target: 16th-8th-16th ISI: 3.2 s ms Meter Standard: Steady Figure DUR: 800 ms 1500 200 ms Target: Played Early ISI: 3.2/1.6 s ms Note. See text for definitions of the quantitative measures. Swartz, Walton, Crummer, Hantz, and Frisina

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The EPOCH and PRESTIMULUS columns are explained in the ERP Recording section below. The oddball paradigm was used in all series, except the Chord series, with 40 targets and 160 standards presented in random sequence for each series. The Chord series followed an equiprobable paradigm where 48 each of target and standard stimuli were presented in random order. In all series the target stimulus was never presented first, nor were two targets ever presented consecutively. The first three series presented to subjects were the Pure Tone, Timbre, and Chord series in random order. The remaining three series were then presented, also in random order. This order was chosen because we hypothesized (correctly for the first two, incorrectly for the third) that SDAT subjects would do best on these series; in the event they were to tire or become distracted, they would then tend not to do so until their "best" responses had been measured. SDAT subjects tended to require more repetitions (up to five) of the sample stimuli than did the healthy controls in order to learn to discriminate the target from the standard. They were also offered breaks in testing after each series, but took them only rarely. Three seven-chord sequences were used for the Chord series. The target sequence is shown in Figure la. It is a melodically and harmonically closed series ending on the tonic chord with the tonic note in both the highest (soprano) and lowest (bass) voices. One of two harmonically open sequences was used for each standard. These sequences differed from the target only by the last chord, being a flatted VI chord (Figure lb) or a diminished vii chord (vii° f of V, Figure 1c). Note that the target and standard chord sequences are three different harmonizations of the same seven note melody in the highest voice. This melody is melodically closed since its last note is the tonic note C. The standards and target are thus both melodically closed in the highest voice, and have only harmonically different endings, either open or closed. Two sequences rather than one were used for the standards so that subjects would be more likely to distinguish not just between different last chords but between the categories of the harmonic function (closed or open) of the last chord. The series consisted of 96 chord sequences, 48 targets, and 24 each of the two standards, presented in random order. All sequences were played an equal number of times in all twelve major keys with the tonic chosen in random order from between C4 (261.6 Hz = middle C) and B 4 (493.9 Hz), eleven semitones higher. Subjects were told that the target sounded like a chord sequence at the end of a song or hymn to help them discriminate it from the standard. In the Interval series the target was an ascending major seventh melodic interval, while the standard was an ascending major second melodic interval. Each interval started from one of the twelve notes between C4 and B 4 selected at random. This was done so that subjects would not distinguish the stimuli on the basis of just the pitch differences between the second notes of the intervals but rather on the basis of the different sizes of the intervals themselves. Subjects were told that the target sounded like two notes farther apart on the piano keyboard than the standard. Three examples of each kind of interval are given in Figures Id (standards) and le (targets). Swartz, Walton, Crummer, Hantz, and Frisina

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The Rhythm series was produced using C4 sampled piano notes. Music notation for the standard and target rhythms in succession is shown in Figure 1 f. For the Meter series the standard consisted of a regular repetition of the three notes (G4-C4-G4, G4 = 392.0 Hz) and the series began with three standards in order to establish the regular meter. The target occurred when the same three note figure was played earlier than expected (the meter was thus shifted or disrupted) two beats after the previous figure rather than the normal four. The beginning of a typical series is shown in Figure lg with a target occurring in the second half of the fourth measure. Subjects were told to listen for the three-note figure to occur earlier than expected and then to press the response button. All stimuli were presented binaurally through Koss headphones in an RF shielded sound proofroom (IAC). The sound level for all was 75 dB SPL ± 2 dB (measured by B&K sound-level meter through a calibrated 6 cc coupler), except for the Chord series which was presented at 82 dB SPL ± 2 dB. For all series, target and standard sounds were played up to five times to subjects to ensure that the perceived differences between the sounds were clear. The target was then repeated, and subjects were instructed to press a response button whenever they heard it again during the series. The pure tones were played with 10 ms linear rise/fall times. For the timbre series a Roland S-50 digital sampling keyboard (30 kHz sampling rate) was used to sample a concert B below middle C (246.9 Hz) from a tuba and a viola. The attack of these sounds was as sampled, while a 10 ms linear decay was added at the end of the stimulus. Sampled piano sounds with 10 ms linear decay were used in the other series. ERP Recording and Performance Measurement To record electrical activity on the scalp, gold-plated surface electrodes were used with an active lead at the Pz site (parietal at the midline), reference electrodes at linked ear lobes, and a ground electrode on the right forehead. Electrode impedance was maintained below 5.0 kOhm. The Pz site was chosen as the recording site because previous topographical studies have shown that the P3 component is maximal at this location for young subjects (Donchin et al., 1986; Hillyard & Picton, 1987; Regan, 1989). For older subjects, the P3 amplitude remains maximal at Pz, although the difference between Pz and other midline locations decreases (Pfefferbaum, Ford, Wenegrat, Roth, & Kopell, 1984; Regan, 1989). Eye movements were monitored by additional electrodes placed at the supraorbital rim and at the lateral canthus of the right eye. Eye movements and behavioral responses were both recorded on a Beckman strip chart recorder. Voltage waveforms were recorded using a Bio-Logic recording and averaging computer (Bio-Logic Systems Corp., Northbrook, IL). Voltages exceeding 98% of the full scale of the A/D converter were rejected automatically on-line. The amplifier gain setting varied from 30,000 to 100,000 so that the artifact rejection level (+/-)correspondingly varied from 81.7 to 24.5 microvolts. Data were recorded with low and high half-amplitude frequency filter settings of 1 and 100 Hz. Neural activity on each trial was recorded and averaged as either a standard or target response independent of performance on the

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trial. To minimize eye-movement artifacts, subjects were requested to remain relaxed and to avoid blinking their eyes while listening to the stimuli. ERP recording epochs and prestimulus recording times varied over the different series. (The recording epoch is the entire length of time over which the ERP is recorded.) These times are listed in Table 1. The EPOCH column lists the recording epochs in milliseconds. The PRESTIMULUS column lists the number of milliseconds prior to the onset of each stimulus at which neural recording began, the prestimulus baseline time. Data Analysis The raw electrophysiological data for our analysis consisted of waveforms averaged over either all target or all standard stimuli (excepting artifact rejections) for each subject for each series and for each of the two days. These averaged waveforms were first digitally filtered with a 6 Hz low-pass filter (3 dB attenuation at 6 Hz, full attenuation at 8 Hz). Each target waveform was then analyzed for P3 ERP features. The latency of the P3 was measured with respect to a target point in the stimulus. This target point was defined as the time at which the target stimulus first differed from the standard stimulus. For the Pure Tone, Timbre, and Meter stimuli, the target point was the same as the time at which each stimulus began (marked SB, the stimulus beginning, on the waveforms in Figure 2). For the Rhythm, Interval, and Chord stimuli, the target point (marked TP on the waveforms in Figure 2) occurred after the beginning of each stimulus. The target point for the Rhythm series occurred 400 ms after the stimulus beginning, halfway through the second note of the target rhythmic figure (Figure If). The target point for the Interval series occurred 500 ms after the stimulus beginning, at the beginning of the second note of the target interval (Figure le). Finally, the target point for the Chord series occurred 3,000 ms after the beginning of the chord sequence, at the beginning of the last chord. The P3 amplitude was then taken to be the maximum voltage above the prestimulus baseline in the Pz target waveform, occurring between 275 and 750 ms latency from the target point for the series. In most cases, the P3 peak showed an apparent difference between the standard and target waveforms and was preceded by Nl, P2, and N2 components. In some cases a prominent P3 feature was apparent in both target and standard waveforms (3.1% for healthy, 14.8% for SDAT). In some other cases (14.5% for healthy, 3.3% for SDAT) there was neither an apparent difference between the target and standard waveforms nor a clear P3 feature. In these latter cases the P3 amplitude was taken to be zero, but all subjects produced P3 features with clear differences between target and standard waveforms on most of the series. Performance was recorded as hits, misses, false alarms, and correct rejections. An overall measure of performance P = (fraction hits + fraction correct rejections ) / 2

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LATENCY Figure 2. Typical ERP waveforms recorded from the Pz site are shown for two individual subjects, one from each group. Points on the target waveforms are marked with the following abbreviations: PS = prestimulus baseline level, SB = stimulus beginning, TP = target point, the time at which the target stimulus first differs from the standard, P3 = P3 peak latency, SE = stimulus end. 106

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was also computed. Here "fraction hits" is the fraction of targets for which the subject correctly pushed the button and "fraction correct rejections" is the fraction of standards for which the subject correctly did not push the button. The measure P varies between 0 and 1. P takes the value 1 for perfect performance. If the subject never presses the button for a target but presses the button for every standard, P takes the value 0. For an oddball series with 160 standards and 40 targets, P has a 95% confidence interval between 0.4 and 0.6 for random responses. Since the P measures constitute percentage data (Myers, 1972), the inverse sine transform P —> Arcsin((P)1/2) was applied before the statistical analyses described below were done. The performance measure P, and P3 amplitudes and latencies were analyzed using repeated measures ANOVAs. While all subjects were tested on two days, several subjects in all groups were unable to complete all the series on both days. A satisfactory repeated measures analysis including Day as a trials factor was, therefore, not feasible. Paired t tests between days for all the different measures in all of the series were thus performed. These tests showed no significant day effect, with p values well above the 0.05 level of significance. All measures were thus averaged over the two days. For each of the three day-averaged dependent variables (performance P, P3 amplitude, and P3 latency) a 5 (series) by 2 (subject group) two way repeated measures ANOVA was conducted. Series was thus a within subjects factor, and subject group was a between subjects factor in the ANOVAs. When the univariate repeated measures F test and the corresponding multivariate F-statistic (Wilk's lambda, the Pillai trace and the Hotelling-Lawley were used) differed, the multivariate result was followed. Because it was not run on all subjects, the meter series was not included in the ANOVAs, but was analyzed separately with t tests (separate variances). When the ANOVAs revealed a significant effect for a given measure, Tukey HSD tests were performed to find which specific differences were significant. Results Representative averaged waveforms for all series, recorded at the Pz site, are shown in Figure 2. These waveforms were recorded from single individuals in each of the two subject groups, except that data for a second SDAT subject are shown for the Chord series. Performance was high for all the waveforms shown for the healthy subject. For the SDAT subjects, performance was high for the Pure Tone, Timbre, and Interval series, but low on the other series (see below). Although not as large as for the healthy subject, the differences between the target and standard waveforms are clear for the SDAT subjects for all but the Chord series. The Chord series also shows only small differences for the healthy subject. As for the healthy subject, the N1-P2-N2 complex of ERP peaks preceding the P3 peak is apparent in most of the SDAT waveforms. The trend towards broader P3 peaks for more complex stimuli, seen for healthy young and older subjects (Chuang et al., 1988) is not, however, apparent in the SDAT waveforms.

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Figure 3. Four waveforms recorded at the Pz site and averaged over responses of SDAT subjects to music stimuli discrimination tasks. The solid line, labeled as in Figure 1, corresponds to the target, and the dotted line to the standard. A P3 component is clearly present in all waveforms despite differences in performance between chance and high levels. Note that waveforms A and D were recorded from the same subject, B and C from two additional subjects. Figure 3 shows a comparison between standard and target waveforms produced by SDAT subjects when performance was either high or at chance levels. (Figures 3a and 3d are the same as those in the SDAT group in Figure 2 but redrawn on a new scale to facilitate intragroup comparison.) Despite the large variations in performance, described as follows, all of the target waveforms are seen to exhibit clear P3 components. Figures 3a and 3b correspond to high performance, with P = 0.96 for Figure 2a and P = 0.95 for Figure 3b. Figure 3c corresponds to poor performance, where P = 0.50 with 0 hits, 40 misses, and 2 false alarms (0% hits and 1% false alarms). Figure 3d also corresponds to poor performance, where P = 0.58, with 11 hits, 29 misses, and 17 false alarms (28% hits and 11% false alarms). Note that the data in Figures 3a and 3d were recorded from the same subject, while the data in Figures 3b and 3c were recorded from two additional subjects. Figure 4 shows plots of proportion of hits versus proportion of false alarms for both subject groups and for the four most difficult series. The Pure Tone and Timbre series are omitted and artificial jitter has been introduced to avoid excessive overlap of data points near the point (0,1). The plots for the two groups suggest different response patterns. While the healthy group exhibits low false alarm rates independent of hit rate except for a few cases, the SDAT group shows a far wider range of hit rates and a wide range of false alarm rates that 108

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