Quarterly Journal of Experimental Psychology
ISSN: 0033-555X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/pqje19
Attention to pure tones Neville Moray , Mike Fitter , David Ostry , Donna Favreau & Vera Nagy To cite this article: Neville Moray , Mike Fitter , David Ostry , Donna Favreau & Vera Nagy (1976) Attention to pure tones, Quarterly Journal of Experimental Psychology, 28:2, 271-283, DOI: 10.1080/14640747608400556 To link to this article: http://dx.doi.org/10.1080/14640747608400556
Published online: 29 May 2007.
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Date: 05 November 2015, At: 13:55
Quarterly Journal of Experimental Psychology (1976) 28, 271-283
ATTENTION TO PURE TONES
t
NEVILLE MORAY," MIKE FITTER, DAVID OSTRY, DONNA FAVREAU AND VERA NAGY
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Department of Psychology, Scarborough College, University of Toronto, Canada Listeners were required to detect increments of intensity or frequency in trains of pure tone bursts under different conditions of attention. The data were analysed taking into account contralateral events when more than one stimulus train was present. Marked changes in d' and /3 were found and the changes were positively correlated. If targets are rare and attention is divided the values of 9, and d' are the same as in undivided attention provided that the contralateral event is a correct rejection, but fall if the contralateral events are hits or false alarms. If targets and nontargets are equi-probable no such difference is found. The data suggest that the observers can make use of the statistical properties of the stimulus sources. The results are compared with those in recent experiments using pure tones in a discrete trial paradigm and in experiments using semantic stimuli.
Introduction Recently Sorkin, Pohlmann and Gilliom (1973) and Fitter (1971, 1974) have drawn attention to a method of analysing multi-channel listening experiments which provides a more detailed view of the data than hitherto, although it was implicit in at least one earlier paper (Shaffer and Hardwick, 1969). I n this paper we will apply the method to a task involving the detection of targets in continuous streams of tone bursts. Sorkin et al. (1973) take up the point made by Garner and Morton (1969) about the measurements needed in two channel experiments to establish either that independence is present or the locus of interaction. Garner and Morton used an information theory analysis which made it advisable to use uncorrelated stimulus sources, whereas Sorkin et al. (1973) used the Theory of Signal Detection (TSD). TSD has the advantage of separating the measurement of the observer's sensitivity from his response bias, and the direct measurement of the latter allows the use of correlated inputs. Sorkin et al. (1973) used a discrete trial, yes-no paradigm requiring the detection of pure tones in noise, and in a dichotic listening experiment analysed observers' performance on each channel contingent on events in the opposite channel in each trial. They found that the presence of a contralateral target reduced the detectability of a tone but had little effect on the response bias,
* Now at the Department of Psychology, University of Stirling, Scotland.
t Now at the MRC Social and Applied Psychology Unit University of 271
Sheffield, England.
N. MORAY, M. FITTER, D. OSTRY, D. FAVREAU AND V. NAGY
Downloaded by [Auburn University Libraries] at 13:55 05 November 2015
272
In this paper we report experiments which fall between Sorkin’s paradigm and that of the more traditional shadowing or monitoring experiments using continuous speech (Treisman and Geffen, 1967; Moray and O’Brien, 1967; Shaffer and Hardwick, 1969). Consider a stream of events, some of them targets requiring the response “yes” and others non-targets requiring the response ‘‘no’’. T h e stimulus-response stream then consists of four classes of events, hits (H), misses (M), false alarms (F), and correct rejections (C). Converting the frequencies to probabilities allows us to calculate values of d‘ and p. In unitary (U) mode there is one message. I n selective (S) mode two messages are presented, one of which is to be processed, - - the other - -ignored. This creates four kinds of stimulus events, TIT, TIT, TIT and TIT, where the first is “a target in message I given a target in message 2”, the second “a target in message I given a non-target in message 2”, and so on. Although the observer is trying to respond only to one message we should break the data into four categories to see if he succeeds. I n divided (D) mode the observer is presented with two messages and responds to both, detecting targets in each. Each stimulus-response class for message I can be paired with four stimulus-response classes for message 2 and vice versa. We can identify H, I H,, H, I F,, H, I M,, and H, I C,, where H, H, is to be read ‘‘a hit on message I given a hit on message 2”, H, I F2is to be read “a hit on message I given a false alarm on message 2”, and so on. T h e events are summarized in Table I.
I
TABLE I Event categories Input-
T Output
Yes No
Input
T/T T/T T/T
T
I
2
3
4
Output
Yes I N o 5
(4
Source
I
2
3
4
6
7
8
(b) Selective mode
Unitary mode
Source
T/T
H
F
H
I
2
F M C
5
6
9
I0
13
I4
2
M 3 7 I1 I5
C 4 8 I2
16
(4 Divided mode
In (U) mode the hit probability is given by I/(I +3). In (S) mode there are two hit probabilities given by 4/(4 +S) and 2 / ( 2 f6). I n (D) mode there are four kinds
ATTENTION TO PURE TONES
273
of hit probability per message, exemplified by I/(I +9), 2/(2+10) and 13/(13+IS). Separating sensitivity and response bias we can use non-independent sources as stimuli to test a model of Moray and Fitter (1973) in which an observer can use his knowledge of the statistical structure of stimulus sequences to direct his attention. If target occurrence is correlated in the stimulus sequences we expect this to be reflected in momentary fluctuations of response bias.
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General procedure T h e following details apply to the first three of four experiments. The same three observers were used in each experiment. The messages were pure tone bursts of IOO ms duration separated by 400 ms inter-burst intervals. A KrohnHite programmable oscillator controlled by an Elliott 903 computer provided tone bursts with preset intensity and frequency. A run consisted of 250 tone bursts per message. T h e non-target tone bursts were about 70 dB re 0*0002microbars. T h e onset and end of each burst had a 25 ms ramp provided by a Grason Stadler electronic switch. T h e probability that a tone burst in a channel would be a target was 0 . 1 . Half the targets occurred at the same moment as a target in the opposite message. An observer heard the stimuli through headphones, sitting in partly sound shielded conditions. Responses were made by pressing one button with the right hand when a target occurred in message I , another button with the left hand when a target occurred in message 2, and both buttons when targets occurred simultaneously. That is, “yes” responses were overt, “no” responses were implicit. Based on earlier data (Moray and O’Brien, 1967; Moray and Fitter, 1974) a response was counted as a hit if it occurred between 150and 1500 ms from stimulus onset. In one message tone bursts were 467 Hz and in the other 1510 Hz. After a target no target would occur for two bursts, and the observers knew this. T h e observers were highly practised. Each experiment was run with conditions in the order (U), (S) and (D). T h e observers were practised to asymptote in each condition. T h e amount of practice following a change in condition was never less than 15 h. Observers practised for 1-5or 3 h per day, depending on their availability. At the end of each practice run the computer printed out hit and false alarm scores and the observer was informed of these. When performance stabilized the test sessions were carried out. T h e test sessions were 1.5 h in length with a break every 20 min. The first two runs of each session were regarded as warmup and were discarded. During the tests the observers were not told their hit and false alarm rates. Instructions were to maximize hits and minimize false alarms. We would emphasize that the results presented are characteristic of highly practised observers (see Ostry, Moray and Marks, 1976). Copies of the raw data can be obtained from the first two authors. Throughout the analysis the following conventions will be used : d’(U) is d‘ in unitary mode d’(S) is d’ in selective mode, while d’ I T and d’ I distinguish moments when there was or was not a target in the rejected message.
274
N. MORAY, M . FITTER, D. OSTRY, D. FAVREAU AND
V.
NACY
d’(D) is d‘ in divided mode while d‘IH, d‘IF, d’IM and d‘IC distinguish moments when the contralateral events were hits, false alarms, misses, and correct rejections respectively. The conventions for p are similar. Experiments I and I1
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Method In Experiment I stimuli were presented monaurally in the (U) condition and dichotically in (D) mode. In all cases 467 HZ tones were presented to the left ear and 1 5 1 0 HZ to the right ear. In Experiment I1 tone bursts were presented binaurally both in (U) and (D) modes, so that messages were separated only by frequency, not by lateralization. Targets were increments of intensity and in a run all the increments were the same size, which was told to the observer at the start of the run. They were the same size in each message in (S) and (D) modes. The size varied randomly by run during the 1-5 h sessions, and could be 2 dB, 3 dB or 4 dB. The data on which the probabilities are based include at least IOO pairs of simultaneous targets for each observer. Results With 4 dB targets the hit rates were so high and the false alarm rates so low that reliable estimates of d‘ and /3 could not be obtained, and so those data have not been included in the following analyses. Qualitatively the pattern seemed similar to that reported below for 2 dB and 3 dB increments, shown in Tables I1 and 111. I n the following “contingency” refers to the nature of the contralateral event (H,F,M,C,T or ??); “separation” refers to Experiment I (monaural or dichotic) or Experiment I1 (binaural); “frequency” distinguishes the 467 Hz and 1 5 1 0 Hz stimuli; and “intensity” refers to the size of the target, 2 dB or 3 dB. T h e analysis is a repeated measures design for three observers. Earlier experiments in selective listening have usually found marked changes in d’ and so we begin with that data. I n unitary mode the only significant factor is intensity ( F = 143.60,df = 1,2, P 4 0.01). Larger increments are more readily detectable. I n selective mode the main effect of intensity and the contingency x intensity interactions are significant ( F = 31-91, df = 1,2, P < 0.05; and F = 77.17, df = 1,2, P < 0.01). Although the main effect of contingency is not significant the interaction suggests that the rejected message is not completely excluded, and is having some effect. With 2 dB increments the presence of a contralateral target is associated with a slightly higher mean d’ than its absence, while with 3 dB targets the effect is reversed. T h e absence of a “separation” effect suggests that selection is based on frequency separation, not on lateralization. Neither d‘ I T nor d’ IT differ significantly from d’(U). When attention is divided between two messages four significant sources of variance appear. These are intensity, ( F = 48.77, df = 1,2, P < o - o ~ )separa, tion ( F = 63-33, df = 1,2, P < 0*02), contingency ( F = 10.25, df = 3,6, P < 0.01) and the contingency x separation interaction ( F = 8.00, df = 3,6,
275
ATTENTION TO PURE TONES
TABLE I1 Values of d' :Experiments I and 11 ~~
Monaural Binaural dB 3 dB 2 dB 3 dB 467Hz 151oHz 4 6 7 H z 1510Hz 4 6 7 H z 151oHz 4 6 7 H z 151oHz 2
-
Unitary mode SI
s2
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s3
3-12 2-34 2.29
2-17
2.62 2-15 1.67 1.50
3'55 2.96
2.32 3'09 1-83 3.78 1-72 2-70
1-64 1-94 1'47
2.41 2.76
1-98 2'73
2'02
1.62 0.80 1-64 0.97
2'77 1'73 1'34 1.24
0.80
1'02
1.11
2.59 2.72 2-26
2'21
1.58
1.99
0.95 1-72 1-34
2.52
1-54
2-08
1-22
2.89 1-51 1.88
2.29 1.46 1-50
2'74 2'41
2'11
4-51 2.56 3'24
2.23 2.04 1.65
3.58 3-07 3.02
1'95 2'33 1.41
Binaural 4'25 3.62 2.41
0.82
2-28
1-74 1-80
3'55 3-20
2.04
1.45
2.05
2-10
2'52 2'1 I
1.72 2.16
1.32 2.30 0'79 1-72
1'73 "44 0.86 1-26
1.40 1.60 0.98 1.88 0.71 1-34
2-09 3-30 1-77 3-35 1-87 2.03 1-74 1-30
1'22
2.08 2'00
2'00
1'94
3'41 2.86 2.69
Selective mode
SI S2
T T T T
S3
T
1.02
1-04 2-30 2.37
Divided mode SI H 1.26
c
S2
S3
F M H C F M H C F M
P < 0.05).
1-80
0-32 2.16 1.22
1.06 0.46 0.99 1-89 1.82 1-39 1'47
Dichotic 5'29 1-95 3.96 1-66 1.30 1.80 1.88 1-22
1.65
1'44 0.72 0.84
2-52 2'00
3'15 3-09 2-29 3.11
2-70 3'55 1-95 3'50 2.61 2-60 1.07 3'51 2'1 I
3-15 1-34 2-91 1-21
2'00 1'10
2.89 1.85 1.39
Since the interaction implies that the contingency factor has different effectson dichotic and binaurally presented messages the data will be separated for further analysis. T h e separation main effect shows that d' in the binaural condition is higher overall than in the dichotic condition (d' = 1-19 vs. 1.63), a finding which agrees with Broadbent (1958) on attention to speech, suggesting that separation may hinder the processing of two messages at once. T h e intensity main effect again, as throughout, indicates that larger increments are more detectable. An inspection of Table I1 suggests a pattern in which there is little difference between d' I H and d' I F, or between d' I C and d' I (U), but that there is a difference between the first and second pairs. Orthogonal comparisons confirm that impression, the difference between the means of the first and second pairs yielding a significant difference (F = 35-93, df = 1,2, P c o - 0 3 ) on the binaural data, and on) the dichotic data. similarly (F = 25.35, df = 1,2,P < O - O ~
N. MORAY, M.
276
FITTER, D. OSTRY, D.
FAVREAU AND V. NAGY
TABLE I11 Values of
p :Experiments I and 11
Monaural Binaural dB 3 dB 2 dB 3 dB 467Hz 1510Hz 467Hz 151oHz 467Hz 151oHz 467Hz 151oHz 2
Unitary mode SI s2
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s3
8-97 17-31 6-90
13.76 10.70 5-85
17.67 44.89 18.00
27.08 15-35 10.42
9'97 8.5 I 3'84
5'23 11.42 50.00
4'36 10.42 2.26 26-10
8-81 19'37
13-93 9.48
13-76 10.58
3'09
7.68 16-55 5'57
11-00
11-69 3'99
Selective mode
SI SZ
T T T T
Divided mode SI H C
F M S2
H C F M
s3
H C F M
2.82 6.62 2'47 6.85
1.88 8-06 1.24 5.65 1'00
4'98 1.04 2'45 I -87 4-63 1'43 2'43
Dichotic 5-61 1'00 7'94 5 '47 1-60 8'43 21.29 21-56 3.96 13-36 6.47 14-77
7'65 14-27 1-31 5'69 1'34 12.27 1.13 2.95 2'39 4'42 1'53 2.58
3-46
Binaural 7.35 1.00 50.50 7-98 3'57 0.83 56-20 71-80 19.82 6-61 '5'94 8.77
2.69 8.12
0.92
1-11
0.81
1.25
0.69 14.89 1'49 0.17 0.78
6-33 0-59
15'35 1-19 7-71 2.66 5.56 I -08 7-18
10.42 0.72 2-13 2.16 4'50 1.09 2.45
13.92
20'52
1'20
13-92 1-96 2-03
1'52
2'44 6.5 I 0.62 4'78
4'52 14-12 2.61 5'72
"53 8.14 I~ 4 6 3'35
1.28
5'65
1-20
0.63
6.33
1'21
2.05
1-72 4'73 0.40 2'75
4-64 1.64 4-05
9.76 7'31 7'94 50.00
23-00 27-37 I .96 18.50 1'74 3'05
27.00 1-39 0.72 1.68 5.71 0.75 4'35
1-08
These results suggest that when attention is divided between two messages the detectability of a target in one message falls only at those moments when a hit or false alarm is made on the second message. When a correct rejection is made on one message detectability on the other is indistinguishable from that seen in unitary mode. We have not discussed d ' I M , performance contingent on a contralateral miss. Throughout our work d' 1 M yields values which fall between those for d' I H and d' I F on the one hand, and those for d' I C on the other. This might occur if on some occasions the target was detected but not reported. An attempt to distinguish these two classes of data in the misses using a latency measure failed. We now turn to j3 where, in contrast to most earlier experiments, large and systematic changes are found. The tables give the raw values of /3, but the analyses of variance are based upon log ( I p), the I being added to make the score always positive (Winer, 1970).
+
ATTENTION TO PURE TONES
277
T h e data in (U) mode show two significant sources of variance, separation
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(F = 31-92, df = 1,2, Pto.05) and the separation x intensity interaction, (F = 25.48, df = 1,2, Pto.05). When single messages are presented binaurally
9, is slightly larger with 3 dB than with 2 dB increments (P = 9’41 vs. 829), but with monaural presentation the difference is very much greater (/3=22*23 vs. 10.58). T h e reason for the difference between unitary monaural and binaural presentation is unclear. I n selective mode there is a significant main effect of separation (F = 36.97, df = I,Z, P
ISSN: 0033-555X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/pqje19
Attention to pure tones Neville Moray , Mike Fitter , David Ostry , Donna Favreau & Vera Nagy To cite this article: Neville Moray , Mike Fitter , David Ostry , Donna Favreau & Vera Nagy (1976) Attention to pure tones, Quarterly Journal of Experimental Psychology, 28:2, 271-283, DOI: 10.1080/14640747608400556 To link to this article: http://dx.doi.org/10.1080/14640747608400556
Published online: 29 May 2007.
Submit your article to this journal
Article views: 19
View related articles
Citing articles: 16 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=pqje19 Download by: [Auburn University Libraries]
Date: 05 November 2015, At: 13:55
Quarterly Journal of Experimental Psychology (1976) 28, 271-283
ATTENTION TO PURE TONES
t
NEVILLE MORAY," MIKE FITTER, DAVID OSTRY, DONNA FAVREAU AND VERA NAGY
Downloaded by [Auburn University Libraries] at 13:55 05 November 2015
Department of Psychology, Scarborough College, University of Toronto, Canada Listeners were required to detect increments of intensity or frequency in trains of pure tone bursts under different conditions of attention. The data were analysed taking into account contralateral events when more than one stimulus train was present. Marked changes in d' and /3 were found and the changes were positively correlated. If targets are rare and attention is divided the values of 9, and d' are the same as in undivided attention provided that the contralateral event is a correct rejection, but fall if the contralateral events are hits or false alarms. If targets and nontargets are equi-probable no such difference is found. The data suggest that the observers can make use of the statistical properties of the stimulus sources. The results are compared with those in recent experiments using pure tones in a discrete trial paradigm and in experiments using semantic stimuli.
Introduction Recently Sorkin, Pohlmann and Gilliom (1973) and Fitter (1971, 1974) have drawn attention to a method of analysing multi-channel listening experiments which provides a more detailed view of the data than hitherto, although it was implicit in at least one earlier paper (Shaffer and Hardwick, 1969). I n this paper we will apply the method to a task involving the detection of targets in continuous streams of tone bursts. Sorkin et al. (1973) take up the point made by Garner and Morton (1969) about the measurements needed in two channel experiments to establish either that independence is present or the locus of interaction. Garner and Morton used an information theory analysis which made it advisable to use uncorrelated stimulus sources, whereas Sorkin et al. (1973) used the Theory of Signal Detection (TSD). TSD has the advantage of separating the measurement of the observer's sensitivity from his response bias, and the direct measurement of the latter allows the use of correlated inputs. Sorkin et al. (1973) used a discrete trial, yes-no paradigm requiring the detection of pure tones in noise, and in a dichotic listening experiment analysed observers' performance on each channel contingent on events in the opposite channel in each trial. They found that the presence of a contralateral target reduced the detectability of a tone but had little effect on the response bias,
* Now at the Department of Psychology, University of Stirling, Scotland.
t Now at the MRC Social and Applied Psychology Unit University of 271
Sheffield, England.
N. MORAY, M. FITTER, D. OSTRY, D. FAVREAU AND V. NAGY
Downloaded by [Auburn University Libraries] at 13:55 05 November 2015
272
In this paper we report experiments which fall between Sorkin’s paradigm and that of the more traditional shadowing or monitoring experiments using continuous speech (Treisman and Geffen, 1967; Moray and O’Brien, 1967; Shaffer and Hardwick, 1969). Consider a stream of events, some of them targets requiring the response “yes” and others non-targets requiring the response ‘‘no’’. T h e stimulus-response stream then consists of four classes of events, hits (H), misses (M), false alarms (F), and correct rejections (C). Converting the frequencies to probabilities allows us to calculate values of d‘ and p. In unitary (U) mode there is one message. I n selective (S) mode two messages are presented, one of which is to be processed, - - the other - -ignored. This creates four kinds of stimulus events, TIT, TIT, TIT and TIT, where the first is “a target in message I given a target in message 2”, the second “a target in message I given a non-target in message 2”, and so on. Although the observer is trying to respond only to one message we should break the data into four categories to see if he succeeds. I n divided (D) mode the observer is presented with two messages and responds to both, detecting targets in each. Each stimulus-response class for message I can be paired with four stimulus-response classes for message 2 and vice versa. We can identify H, I H,, H, I F,, H, I M,, and H, I C,, where H, H, is to be read ‘‘a hit on message I given a hit on message 2”, H, I F2is to be read “a hit on message I given a false alarm on message 2”, and so on. T h e events are summarized in Table I.
I
TABLE I Event categories Input-
T Output
Yes No
Input
T/T T/T T/T
T
I
2
3
4
Output
Yes I N o 5
(4
Source
I
2
3
4
6
7
8
(b) Selective mode
Unitary mode
Source
T/T
H
F
H
I
2
F M C
5
6
9
I0
13
I4
2
M 3 7 I1 I5
C 4 8 I2
16
(4 Divided mode
In (U) mode the hit probability is given by I/(I +3). In (S) mode there are two hit probabilities given by 4/(4 +S) and 2 / ( 2 f6). I n (D) mode there are four kinds
ATTENTION TO PURE TONES
273
of hit probability per message, exemplified by I/(I +9), 2/(2+10) and 13/(13+IS). Separating sensitivity and response bias we can use non-independent sources as stimuli to test a model of Moray and Fitter (1973) in which an observer can use his knowledge of the statistical structure of stimulus sequences to direct his attention. If target occurrence is correlated in the stimulus sequences we expect this to be reflected in momentary fluctuations of response bias.
Downloaded by [Auburn University Libraries] at 13:55 05 November 2015
General procedure T h e following details apply to the first three of four experiments. The same three observers were used in each experiment. The messages were pure tone bursts of IOO ms duration separated by 400 ms inter-burst intervals. A KrohnHite programmable oscillator controlled by an Elliott 903 computer provided tone bursts with preset intensity and frequency. A run consisted of 250 tone bursts per message. T h e non-target tone bursts were about 70 dB re 0*0002microbars. T h e onset and end of each burst had a 25 ms ramp provided by a Grason Stadler electronic switch. T h e probability that a tone burst in a channel would be a target was 0 . 1 . Half the targets occurred at the same moment as a target in the opposite message. An observer heard the stimuli through headphones, sitting in partly sound shielded conditions. Responses were made by pressing one button with the right hand when a target occurred in message I , another button with the left hand when a target occurred in message 2, and both buttons when targets occurred simultaneously. That is, “yes” responses were overt, “no” responses were implicit. Based on earlier data (Moray and O’Brien, 1967; Moray and Fitter, 1974) a response was counted as a hit if it occurred between 150and 1500 ms from stimulus onset. In one message tone bursts were 467 Hz and in the other 1510 Hz. After a target no target would occur for two bursts, and the observers knew this. T h e observers were highly practised. Each experiment was run with conditions in the order (U), (S) and (D). T h e observers were practised to asymptote in each condition. T h e amount of practice following a change in condition was never less than 15 h. Observers practised for 1-5or 3 h per day, depending on their availability. At the end of each practice run the computer printed out hit and false alarm scores and the observer was informed of these. When performance stabilized the test sessions were carried out. T h e test sessions were 1.5 h in length with a break every 20 min. The first two runs of each session were regarded as warmup and were discarded. During the tests the observers were not told their hit and false alarm rates. Instructions were to maximize hits and minimize false alarms. We would emphasize that the results presented are characteristic of highly practised observers (see Ostry, Moray and Marks, 1976). Copies of the raw data can be obtained from the first two authors. Throughout the analysis the following conventions will be used : d’(U) is d‘ in unitary mode d’(S) is d’ in selective mode, while d’ I T and d’ I distinguish moments when there was or was not a target in the rejected message.
274
N. MORAY, M . FITTER, D. OSTRY, D. FAVREAU AND
V.
NACY
d’(D) is d‘ in divided mode while d‘IH, d‘IF, d’IM and d‘IC distinguish moments when the contralateral events were hits, false alarms, misses, and correct rejections respectively. The conventions for p are similar. Experiments I and I1
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Method In Experiment I stimuli were presented monaurally in the (U) condition and dichotically in (D) mode. In all cases 467 HZ tones were presented to the left ear and 1 5 1 0 HZ to the right ear. In Experiment I1 tone bursts were presented binaurally both in (U) and (D) modes, so that messages were separated only by frequency, not by lateralization. Targets were increments of intensity and in a run all the increments were the same size, which was told to the observer at the start of the run. They were the same size in each message in (S) and (D) modes. The size varied randomly by run during the 1-5 h sessions, and could be 2 dB, 3 dB or 4 dB. The data on which the probabilities are based include at least IOO pairs of simultaneous targets for each observer. Results With 4 dB targets the hit rates were so high and the false alarm rates so low that reliable estimates of d‘ and /3 could not be obtained, and so those data have not been included in the following analyses. Qualitatively the pattern seemed similar to that reported below for 2 dB and 3 dB increments, shown in Tables I1 and 111. I n the following “contingency” refers to the nature of the contralateral event (H,F,M,C,T or ??); “separation” refers to Experiment I (monaural or dichotic) or Experiment I1 (binaural); “frequency” distinguishes the 467 Hz and 1 5 1 0 Hz stimuli; and “intensity” refers to the size of the target, 2 dB or 3 dB. T h e analysis is a repeated measures design for three observers. Earlier experiments in selective listening have usually found marked changes in d’ and so we begin with that data. I n unitary mode the only significant factor is intensity ( F = 143.60,df = 1,2, P 4 0.01). Larger increments are more readily detectable. I n selective mode the main effect of intensity and the contingency x intensity interactions are significant ( F = 31-91, df = 1,2, P < 0.05; and F = 77.17, df = 1,2, P < 0.01). Although the main effect of contingency is not significant the interaction suggests that the rejected message is not completely excluded, and is having some effect. With 2 dB increments the presence of a contralateral target is associated with a slightly higher mean d’ than its absence, while with 3 dB targets the effect is reversed. T h e absence of a “separation” effect suggests that selection is based on frequency separation, not on lateralization. Neither d‘ I T nor d’ IT differ significantly from d’(U). When attention is divided between two messages four significant sources of variance appear. These are intensity, ( F = 48.77, df = 1,2, P < o - o ~ )separa, tion ( F = 63-33, df = 1,2, P < 0*02), contingency ( F = 10.25, df = 3,6, P < 0.01) and the contingency x separation interaction ( F = 8.00, df = 3,6,
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TABLE I1 Values of d' :Experiments I and 11 ~~
Monaural Binaural dB 3 dB 2 dB 3 dB 467Hz 151oHz 4 6 7 H z 1510Hz 4 6 7 H z 151oHz 4 6 7 H z 151oHz 2
-
Unitary mode SI
s2
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s3
3-12 2-34 2.29
2-17
2.62 2-15 1.67 1.50
3'55 2.96
2.32 3'09 1-83 3.78 1-72 2-70
1-64 1-94 1'47
2.41 2.76
1-98 2'73
2'02
1.62 0.80 1-64 0.97
2'77 1'73 1'34 1.24
0.80
1'02
1.11
2.59 2.72 2-26
2'21
1.58
1.99
0.95 1-72 1-34
2.52
1-54
2-08
1-22
2.89 1-51 1.88
2.29 1.46 1-50
2'74 2'41
2'11
4-51 2.56 3'24
2.23 2.04 1.65
3.58 3-07 3.02
1'95 2'33 1.41
Binaural 4'25 3.62 2.41
0.82
2-28
1-74 1-80
3'55 3-20
2.04
1.45
2.05
2-10
2'52 2'1 I
1.72 2.16
1.32 2.30 0'79 1-72
1'73 "44 0.86 1-26
1.40 1.60 0.98 1.88 0.71 1-34
2-09 3-30 1-77 3-35 1-87 2.03 1-74 1-30
1'22
2.08 2'00
2'00
1'94
3'41 2.86 2.69
Selective mode
SI S2
T T T T
S3
T
1.02
1-04 2-30 2.37
Divided mode SI H 1.26
c
S2
S3
F M H C F M H C F M
P < 0.05).
1-80
0-32 2.16 1.22
1.06 0.46 0.99 1-89 1.82 1-39 1'47
Dichotic 5'29 1-95 3.96 1-66 1.30 1.80 1.88 1-22
1.65
1'44 0.72 0.84
2-52 2'00
3'15 3-09 2-29 3.11
2-70 3'55 1-95 3'50 2.61 2-60 1.07 3'51 2'1 I
3-15 1-34 2-91 1-21
2'00 1'10
2.89 1.85 1.39
Since the interaction implies that the contingency factor has different effectson dichotic and binaurally presented messages the data will be separated for further analysis. T h e separation main effect shows that d' in the binaural condition is higher overall than in the dichotic condition (d' = 1-19 vs. 1.63), a finding which agrees with Broadbent (1958) on attention to speech, suggesting that separation may hinder the processing of two messages at once. T h e intensity main effect again, as throughout, indicates that larger increments are more detectable. An inspection of Table I1 suggests a pattern in which there is little difference between d' I H and d' I F, or between d' I C and d' I (U), but that there is a difference between the first and second pairs. Orthogonal comparisons confirm that impression, the difference between the means of the first and second pairs yielding a significant difference (F = 35-93, df = 1,2, P c o - 0 3 ) on the binaural data, and on) the dichotic data. similarly (F = 25.35, df = 1,2,P < O - O ~
N. MORAY, M.
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FITTER, D. OSTRY, D.
FAVREAU AND V. NAGY
TABLE I11 Values of
p :Experiments I and 11
Monaural Binaural dB 3 dB 2 dB 3 dB 467Hz 1510Hz 467Hz 151oHz 467Hz 151oHz 467Hz 151oHz 2
Unitary mode SI s2
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s3
8-97 17-31 6-90
13.76 10.70 5-85
17.67 44.89 18.00
27.08 15-35 10.42
9'97 8.5 I 3'84
5'23 11.42 50.00
4'36 10.42 2.26 26-10
8-81 19'37
13-93 9.48
13-76 10.58
3'09
7.68 16-55 5'57
11-00
11-69 3'99
Selective mode
SI SZ
T T T T
Divided mode SI H C
F M S2
H C F M
s3
H C F M
2.82 6.62 2'47 6.85
1.88 8-06 1.24 5.65 1'00
4'98 1.04 2'45 I -87 4-63 1'43 2'43
Dichotic 5-61 1'00 7'94 5 '47 1-60 8'43 21.29 21-56 3.96 13-36 6.47 14-77
7'65 14-27 1-31 5'69 1'34 12.27 1.13 2.95 2'39 4'42 1'53 2.58
3-46
Binaural 7.35 1.00 50.50 7-98 3'57 0.83 56-20 71-80 19.82 6-61 '5'94 8.77
2.69 8.12
0.92
1-11
0.81
1.25
0.69 14.89 1'49 0.17 0.78
6-33 0-59
15'35 1-19 7-71 2.66 5.56 I -08 7-18
10.42 0.72 2-13 2.16 4'50 1.09 2.45
13.92
20'52
1'20
13-92 1-96 2-03
1'52
2'44 6.5 I 0.62 4'78
4'52 14-12 2.61 5'72
"53 8.14 I~ 4 6 3'35
1.28
5'65
1-20
0.63
6.33
1'21
2.05
1-72 4'73 0.40 2'75
4-64 1.64 4-05
9.76 7'31 7'94 50.00
23-00 27-37 I .96 18.50 1'74 3'05
27.00 1-39 0.72 1.68 5.71 0.75 4'35
1-08
These results suggest that when attention is divided between two messages the detectability of a target in one message falls only at those moments when a hit or false alarm is made on the second message. When a correct rejection is made on one message detectability on the other is indistinguishable from that seen in unitary mode. We have not discussed d ' I M , performance contingent on a contralateral miss. Throughout our work d' 1 M yields values which fall between those for d' I H and d' I F on the one hand, and those for d' I C on the other. This might occur if on some occasions the target was detected but not reported. An attempt to distinguish these two classes of data in the misses using a latency measure failed. We now turn to j3 where, in contrast to most earlier experiments, large and systematic changes are found. The tables give the raw values of /3, but the analyses of variance are based upon log ( I p), the I being added to make the score always positive (Winer, 1970).
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277
T h e data in (U) mode show two significant sources of variance, separation
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(F = 31-92, df = 1,2, Pto.05) and the separation x intensity interaction, (F = 25.48, df = 1,2, Pto.05). When single messages are presented binaurally
9, is slightly larger with 3 dB than with 2 dB increments (P = 9’41 vs. 829), but with monaural presentation the difference is very much greater (/3=22*23 vs. 10.58). T h e reason for the difference between unitary monaural and binaural presentation is unclear. I n selective mode there is a significant main effect of separation (F = 36.97, df = I,Z, P
