A second experiment showed that the effect was due to noise interacting with task priority and not with the identity of the task performed first rather than second.
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Acta Psychologica 5 1 (1982) 245-255 North-Holland Publishing Company
THE EFFECTS OF NOISE AND TASK PRIORITY OF ORDER AND LOCATION Andrew
P. SMITH
ON RECALL
*
Uniuersity of Oxford, UK
Accepted
December
198 1
Previous studies have suggested that one of the effects of noise is to improve performance on a primary task and impair performance on a secondary task. This was confirmed in the first experiment which used a modified version of Hockey and Hamilton’s (1970) task of memory for order and location. A second experiment showed that the effect was due to noise interacting with task priority and not with the identity of the task performed first rather than second. The effect of priority can easily be modified and a third experiment showed that priority instructions have to be effective for there to be an interaction between noise and priority. It is suggested that a major effect of noise is to bias the allocation of effort towards the operation which appears to best repay the investment of more effort. This may take the form of a bias towards the high priority task but the effect of noise is also likely to depend on other factors such as the difficulty of each part of the task and the salience of the stimuli.
Broadbent (1971) suggested that noise increases the probability of sampling information from dominant sources at the expense of nondominant ones. This suggestion was based on several pieces of evidence which were current at the time but now seem more doubtful. The first line came from studies of the effects of noise on dual task performance. These will now be briefly reviewed and in the following account noise levels and weightings are as reported in the original articles. Hockey (1970a, b) showed that 100 dB noise improved performance on a central tracking task but produced less efficient reactions to lights from a visual display which were seen as presenting signals with a lower probability. However, Forster and Grierson (1978) carried out four studies using 92 dBA noise which were aimed at extending and replicating Hockey’s results. In one experiment they attempted to use the same * Author’s address: Parks Road, Oxford
A.P. Smith, Dept. of Experimental OX1 3UD, UK.
0001-69 1S/82/0000-0000/$02.75
Psychology,
0 1982 North-Holland
University
of Oxford,
South
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signal frequencies and priorities through instructions as Hockey’s main study but they were unable to replicate Hockey’s findings. Hartley (1981) has argued that Forster and Grierson’s attempt to replicate Hockey lacked experimental power in that they used a small number of subjects (eight subjects). He showed that similar results to Hockey’s could be obtained, but Hartley’s results also differed from Hockey’s in certain respects and this reflects differences in the actual tasks used. Even if one ignores the lack of power in Forster and Grierson’s experiments one might still have expected a difference between their results and Hockey’s This is because they used a much more difficult tracking task (average performance was about 33% time on target) than did Hockey (60-70% on target). Again, Loeb and Jones (1978) found that 105 dBA noise impaired the tracking task rather than the reaction to the lights. As Hockey had already shown that the effects of noise varied with the probability that a particular source required attention one might explain the discrepant results in terms of differences in task parameters. All these later results suggest that noise does not always act in a passive way biasing performance towards the high priority task but that its effect is determined by a complex combination of such factors as dominance set by instructions, difficulty of each part of the task and probability of needs for action. The second line of evidence to support Broadbent’s statement comes from studies of the effects of noise on the Stroop task. In one condition of the Stroop task subjects are asked to name the colour of the ink in which irrelevant colour names are printed. The irrelevant colour names produce interference and subjects are much slower in this condition than when they merely have to name the colours with no irrelevant words. Studies by Houston and Jones (1967) and Houston ( 1969) have shown that noise may reduce the amount of interference from the words. However, the effect of noise on the Stroop task is inconsistent and there have been studies which have shown an increase in interference in noise (Hartley and Adams 1974: exp. 1) and others which have shown that the effect changes with the duration of the noise (Hartley and Adams 1974: exp. 2). Recently, Broadbent (1980) has shown that previous exposure to 85 dBC (78 dBA) noise affects the control conditions of the Stroop task (with the colour/word ratio being reduced after noise) but not the interference conditions. In studies still to be reported Smith and Broadbent have shown that a similar effect occurs when the task is performed in noise rather than after it. As the
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amount of interference depends on the relative speed of naming the colours and the colour names one can see that different effects of noise on the interference condition could be obtained depending on the initial speeds of the simple conditions. In other words the effects of noise and also the ‘after effects’ of noise on the Stroop task can be explained without resorting to a theory of allocation of attention between two tasks. A third line of research that supports Broadbent’s statement is Eysenck’s (1975) finding that 80 dB noise exaggerated the difference between recalling dominant and non-dominant instances of categories from semantic memory. Smith and Broadbent (1982) found that the effect of 85 dBC (78 dBA) noise on recall of category instances depended on the retrieval strategies being used. It may be profitable to consider another way of looking at the phenomena which Broadbent interpreted as due to dominance. They could rather be explained by choice of strategy. Broadbent’s statement referred largely to studies using levels of noise over 95 dB. Recent studies, such as Eysenck’s, have shown that effects may be obtained using 80-85 dB noise. Many tasks which show an effect of this moderate intensity noise have used verbal materials and this made it attractive to consider noise effects in terms of masking of inner speech (Poulton 1977). Broadbent (1978) has argued that there is strong evidence against an internal mechanism similar to masking, and internal speech appears to be a motor rather than sensory phenomenon. More generally, tasks using verbal materials present the subjects with several strategies of performance. The different patterns of noise effects could be due to effort being directed to one aspect of the task rather than another. Such a way of looking at noise effects enables one to link studies using moderate intensity noise with effects like Hockey’s found only at higher noise levels. Indeed, Hockey and Hamilton (1970) demonstrated an effect of 80 dB noise on short-term memory which they linked with the selective effect of noise found at higher intensities. Hockey and Hamilton (1970) found that 80 dB noise impaired recall of task irrelevant, ‘incidental’ information. In their experiment the subjects were instructed to recall the order of eight words. Each word was presented in one of the four comers of the screen (two words per location) and after the subjects had recalled the words in order they were then asked to recall which location the words had been presented in. Subjects working in noise recalled significantly fewer correct loca-
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tions than a control group working in quiet (32% v. 48.5%) but were better at recalling the order of words (this effect just missed significance, p = 0.055). Davies and Jones (1975) were able to replicate the poorer recall of location using 95 dBA noise but found no significant effect of noise on recall of order information. Similar results showing impaired recall of incidental information in noise have been found by O’Malley and Poplawsky (197 1) using both 85 dB and 100 dB noise, and Cohen and Lezak (1977) using 95 dBA noise. Niemi et al. (1977) were unable to replicate Hockey and Hamilton’s results. This suggests that, like the effects of noise on the tracking and lights task, background conditions are very important in determining the effects of noise on memory for order and location. Hockey and Hamilton’s technique has certain weaknesses which make interpretation difficult. These have already been discussed in detail elsewhere (Daee and Wilding 1977; Fowler and Wilding 1979) but they will be briefly mentioned because they show why the experiments reported in this article used a modified version and why certain experimental manipulations were carried out. The first problem with the Hockey and Hamilton technique is that recall of location depended on prior item recall. Secondly, as the primary task was carried out first it is unclear whether noise is interacting with primary/secondary tasks or with first/second tasks. Hockey and Hamilton’s results have not been extended to see whether the noise effect still occurs when location is primary and order secondary, nor has any attempt been made to see whether the effects change with practice. It is impossible to test this last point using an incidental learning paradigm because once the subject has carried out the task for the first time recall of location will no longer be incidental. The first experiment attempted to replicate Hockey and Hamilton’s result using a modified version of their task which eliminated some of the above weaknesses. It also attempted to extend the original findings to see whether the same effect of noise was obtained when location was primary and order secondary. Experiment
1
Method Subjects The Ss were 45 female members of the Oxford Subject Panel and they were paid for participating in the experiment. Each S was tested individually and the noise and quiet sessions were at the same time of day.
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Procedure Ss were instructed that they would be shown eight words and that each word would be shown in one of four locations on the screen. They were informed that they were going to have to recall the order the words were presented in and the location where each word had been shown. One group of Ss (n =25) were instructed that their main aim was to recall the order of the words and that they would do this before they recalled the location. Another group (n =20) were told that recall of location was their main aim and that they would do this before they recalled the order. The Ss were instructed that after the words had been presented they would be given an answer sheet which would have the eight words typed at the side. In the order recall part of the task they had to put the word which had been shown first against number 1, the word that had been shown second against number 2, and so on. In the location recall part the four locations were indicated by lines and the Ss had to write each word under the line that corresponded to the position where the word had been presented. Each word was presented on the screen for 2 set, and was presented in one of four locations across the centre of the screen. After the words had been presented the Ss were given the answer sheets. The eight words were typed down the side of the sheet in a pseudo-random order, the constraint being that no word was in the same ordinal position as it had been presented in. When Ss had completed their primary task they then moved on to the secondary part. They had been instructed to use all eight words in both parts even if they felt that they were guessing. By providing the Ss with the eight words recall of order and location could be assessed independently of item recall. Each S carried out the task in both noise and quiet. A different set of words was used in each session and the two sessions were a week apart. Half the Ss had the noise treatments in the order quiet-noise and half in the order noise-quiet. It was possible to give each S the task twice because the incidental learning task had been replaced by one in which the parts were primary or secondary according to instructions. Natup of the Noise Freefield noise was played during both presentation and recall and the sound level was 85 dBC (78 dBA) with equal levels per octave (* 1 dB) from 125-4000 Hz. The sound level in the quiet condition was 60 dBC (50 dBA). Results The mean percentage of words correct in both parts of the task is shown for the order/primary and location/primary groups in table 1. It can be seen that in noise Ss performed better at the primary task but worse at the secondary. This was true for both the order/primary and location/primary groups. An analysis of variance distinguishing the between S factors of order/primary v. location/primary and the order of noise treatments, and the within Ss factors of noise conditions and primary/secondary tasks showed that the noise X primary/secondary task interaction was highly significant (F( 1,41)= 8.07, p =0.007). There was, of course, a significant effect of primary/secondary tasks (F( 1,41) = 33,49, p
