et al. 1971). In certain conditions attended task relevant auditory stimuli may also elicit a late positive component or P3 wave (Sutton et al. 1965. 1967: Wilkinson ...
Electroencephalography and Clinical Neurophx'siolog3. 1974. 36:191 199 Else~'ier Scientific Publishing Compan.,,. Amsterdam Printed in The Netherlands
191
HUMAN AUDITORY EVOKED POTENTIALS. II: EFFECTS OF ATTENTION ~ T . W . PiCTON AND S. A. HII.I.YARD Department of Neuroxcie.~u'es, ! 'nh'ersitv ol Colilon~ia, San Die~lo, La ,hdla, Calif. 92037 ¢ U.S..4. )
tAccepted for publication:August 22, 1973~
Auditory attention involves the selective perception of a particular auditory message and the relative suppression of competing sensory information. Neurophysiological theories of auditory attention have ranged l¥om selective peripheral gating prior to sensory analysis (e.,q,, HernandezPeon 1966), to a more central selective response to tho,~ stimuli evaluat~xt as signilicant after sensoD' analysis (e,,q., Sokolov 1963). One approach to determining the neural mechanism of this stimulus-selection process is to study the influence of different attentive strategies upon the components of the human auditory evoked potential. The "'early" (0-8 msec) and "'middle" (8 50 msec) latency components have been found to be stable during fluctuations in subjective arousal and environmental conditions {Mendel and Goldstein 1969, 197 ! : Jewett and Williston 197 ! ; Amadeo and Shagass 1973). but have not been examined during changes in the direction of selective attention. Directing attention toward an auditory stimulus has consistently been reported to enhance the N~ (90 msec) P_, (170 msec) components ofthe evoked response (Davis 1964: Gross et al. 1965; Satterfield 1965; Spong et ai. 1965; Wilkinson and Morlock 1967; Hirsch 1971; Keating and Ruhm 1971: Picton et al. 1971). In certain conditions attended task relevant auditory stimuli may also elicit a late positive component or P3 wave (Sutton et al. 1965. 1967: Wilkinson and Morlock 1967; Ritter and Vaughan 1969: Sheatz and Chapman 1969; Smith et al. 1970; Hillyard et al. 1971:
K arlin et ai, 1971 ; Picton et al. 1973). The present study examines the effects of alteration upon the human auditory evoked potentials recorded concurrently from all levels of the auditory system so as to delineate those levels at which different stimulus selection processes t..ke place. MI~rll('II)S
Paid students, age 20-30, most of whom were quite familiar with the techniques and requirements of evoked potential recording, served as subjects for this experiment. They sat in a comfortable chair in a sound attenuated room, and adjusted their posture so that little or no muscle activity was observed in the EEG monitored on an oscilloscope. 60 dB SL 50 #sec "'standard" clicks were presented to the subject's right ear through earphones at a rate of once a second. Every 5-30 sec the intensity of a single click ("signal") was lowered by a fixed amount, which was between 1 and 5 dB for different subjects. During the "'attend" condition, the subject was asked to detect and count the signals in a block of ! 100 stimuli. The signal intensity was adjusted so that the subject could detect between 80 and 950. of the signals. During the "'ignore" condition the subject read a book and was instructed to disregard as much as possible the ongoing auditory stimuli. Attend and ignore conditions were presented in a balanced manner so as to rule out any possible order effects. One subject underwent il paired attend-ignore conditions, another subject 6, four subjects underwent 4 pairs, and two subjects 2 pairs. The experiment t This investigation was supported by NASA Grant No. .took several hours to complete and most sub05-009-198 and NIH Grant No USPHS NS 10482-01 awarjects spread the recording sessions over 2 or 3 ded to Professor Galambos. the Medical Research Council days. of Canada. and the Sloan Foundation
192 There were two modifications to this basic experimental paradigm. For two subjects the experiment was repeated using more frequent signal clicks (every 1-10 stimuli, on the average 1 in 5). This allowed more detailed examination of the evoked response to the signal. In a final experiment the signal stimulus was changed from a lower intensity click to a complete absence of any stimulus. This allowed examination of the evoked response to a detected omitted stimulus. The evoked potential over the first 50 rasec after the standard st imulus was recorded between vertex and right mastoid electrodes, amplified on a Grass P 15 preamplifier (30-3 kc/sec) and a Tektronix FMI22 amplifier {8-10 kc/sec)and averaged online on a Fabritek 1052 Signal Averager. EEG activity from Pz. Cz. Fz electrodes referred to a left mastoid reference and a vertical electrooculogram (EOG) were amplified on a Grass IVlodel 6 Polygraph (frequency ban@ass 1+70 c/see) and recorded on FM tape for later off-line analysis o1" tlae longer latency components of the evoked potential to either standard or signal stimuli. Examination of the early components of the evoked potential to the signal stimulus was done by recording all EEG activity on high speed FM tape (0-2.5 kc/sec) and averaging off-line using different computer analysis periods. The scalp distribution of the evoked response to a detected stimulus omission was evaluated in seven subjects using the 16channel averaging technique described in the preceding paper.
1. %V. PICTON AND S. A. HILLYARD
measured for each.of the attend and ignore conditions. The amplitude measurements were cbp,x~crted to percentages of the mean ignore condition for each subject prior to statistical analysis in order to remove intersubject variability. If the resultant distributions were approximately normal a t-test comparison was performed. Otherwise (i.e., for Waves VI, No, Po), a Wilcoxon signed rank analysis was used. The results are delineated in Table I. All significance levels below 0.05 are shown, although since fifteen measurements are being compared only significance levels below 0.0033 should be considered as meaningful {Hays 1963, p. 489). TABLEI Effect of attention on components of evoked potential.
Component
Latency (msec)
1 _+
I! + lit +_ IV ± V _ V! _+
RESULTS
N,~ _+ Po
Ez,okedpo ten I h7l~"to s tat ~cks:'d clicks
Fifteen distinct components o1" the auditory evoked potential could be consistently recognized in all subjects. The identification and nomenclature of these components have been reviewed in the previous paper. A baseline was determined from the first 0.5 msec of the response and extended through the succeeding evoked potential components. If such a baseline was too difficult to evaluate because of stimulus artifact contamination, an arbitrary baseline was drawn at the midpoint between the troughs following components I and II. The baseline to peak amplitude and the latency of each component was
+ N~ • -+
P,, Nh Pn Nn
P., N_,
1.5 ,)._'~
r
2.6 0.1 3.8 0.3 5.0 0.5 5,8 0,3 7,4 0,4 8.9 0.7 12 ! 16 I
25 • _+ 2 36 +- 3 50 +- 4 83 -+ 7 161 +- 17 290 + 47
Amplitude {ttV } ............................... Attend Ignore
Significance
0.2~ _+0.2~
N.~
0.21 +_014 0.41 +0.23 0.47 +0.28 0.52 +_0.29 0,21 +0~11 0.21 +0.15 0.08 +0,09 0,34 ~0.17
0,62 _+0.36 0.49 _+0.30 0.60 _+0.41 [..58 +-0,89 3.58 +- 1.07 2.02 +1.09
tt._'+, tt I.',
tJ,24 +0.15 Ns 0.38 +0.14 Ns 0,40 +0.19 Ns 0.46 _+0,23 Ns 0,18 +0,09 Ns 0.19 +0.17 Ns 0.08 +_0.07 Ns 0,29 +_0.19 P
