- Email: [email protected]
The acoustic similarity effect
Acta Psychologica 0 North-Holland
SHORT
39 (1975), 237-239. Publishing Company.
COMMUNICATION
THE ACOUSTIC
SIMILARITY
EFFECT
Donald MARCER Dept. of Psychology,
Received
January
University of Southampton,
U.K.
1975
The latency of reading 5-word sequences of 3 levels of acoustic similarity was measured. Highly similar sequences were found to have longer latencies than sequences of low similarity or control sequences. The implications of this finding for the acoustic similarity effect in STM are discussed.
It is generally held that verbal material is coded into STM on an acoustic basis. This was demonstrated by Conrad (1962) who showed that errors in the immediate recall of visually presented consonants showed a significant overlap with listening errors for consonants presented in white noise. Similarly Wickelgren (1965) found that errors in the recall of 8-item consonant-letter sequences tended to be of an acoustic nature. Wickelgren (1966) also showed that both RI and PI in STM increase with the phonemic similarity of the interfering material. Baddeley and Dale (1966) have shown that while long-term forgetting of words is related to semantic similarity, it is acoustic similarity that predicts STM loss. Although the acoustic similarity phenomenon has been widely demonstrated, attempts to isolate where in the information processing system (i.e. input, storage or retrieval) the effect occurs have proved less successful. Conrad et al. (1966) were among the first to try to answer this question. They measured the retention of 6-consonant sequences of high or low intra-sequence similarity presented at either 60 or 120 consonants per minute. In all cases the similar sequences showed the worst recall, but there was no rate by similarity interaction. This latter finding led the authors to conclude that the effect was not due to a limitation of the rate at which the encoding system can process
238
II. Marcer /Acoustic
similarity effect
information. However, as correct recall of the similar items in the slow condition was only 18%, it is possible that any interaction was being masked by a ‘floor effect’. In a more detailed investigation Baddeley (1968) again rejected the input deficit hypothesis. He based this conclusion on a finding that STM for word sequences was not attenuated when the level of background noise was increased. Baddeley then presented data which he claimed locates the effect at retrieval. However, whatever the merits of this last claim, Peterson and Johnson (1971) claim that at least part of the effect is dependent on the encoding stage. They found that the superior recall of low-similarity visually-presented messages was eliminated when articulation at input was minimised. Clearly, the extent to which the acoustic similarity effect is located at input is still uncertain. One of the main problems of employing memory experiments to clarify the position is that these effects have to be isolated from those associated with storage or retrieval. The experiment reported here overcame this by measuring how quickly subjects were able to read Sword sequences which differed in their intrasequence acoustic similarity.
Method Using a counterbalanced design 30 Ss read to themselves, as quickly as possible, 15 sequences, each of 5 words. The sequences were of high, low or zero acoustic similarity (HAc, LAc, ZAc). Each sequence was presented as a 5-word unit in a memory drum. The onset of presentation activated a timer which was stopped via a throat microphone when S indicated that he had read the sequence by saying ‘yes’. It was emphasized that, while he must act as quickly as possible, S should be quite sure that he had recognised every word. 3 practice trials were given.
Material Examples of the word sequences are: HAc: tap, pan, fat, fan, pat; LAc: top, pun, pat; ZAc: met, nip, cog, gap, bus. Sequences were matched for word frequency.
fit, fen,
Results The mean latency of responding was HAc = 2.705 set, LAc = 2.375 set and ZAc = 2.382 sec. A repeated measures analysis of variance showed word sequence to be significant at beyond
D. Marcer /Acoustic
similarity effect
239
the 0.1% level (F= 10.60, df 14,406). Scheffe tests showed this to be due entirely to the HAc latency being greater than in the other two conditions which did not differ. In no case was a HAc sequence read more quickly than either a LAc or a ZAc sequence.
Discussion The implications of this experiment can be simply stated. A sequence which is made up of words which are very similar acoustically needs more time to read than one where the items are dissimilar. It follows that if two such sequences are used as stimuli in an STM experiment using visual presentation and equal presentation intervals, then the similar sequence will have less processing time available for each word (according to this experiment about 12% less). This in turn would produce lower levels of learning, with a corresponding lower level of recall, and hence a typical acoustic similarity effect. It remains to be determined to what extent the effect would persist if input levels were equated.
References Baddeley, A. D., 1968. How does acoustic similarity affect short-term memory? Quart. .I. Exp. Psychol. 20,249-264. Baddeley, A. D., H. C. A. Dale, 1966. The effect of semantic similarity on retroactive interference in long- and short-term memory. J. Verb. Learn. Verb. Behav. 5,417-420. Conrad, R., 1962. An association between memory errors and errors due to acoustic masking of speech. Nature 193, 1314-1315. Conrad, R., A. D. Baddeley, A. J. Hull, 1966. Rate of presentation and the acoustic similarity effect in short-term memory. Psychon. Sci. 5, 233-234. Peterson, L. R., S. T. Johnson, 1971. Some effects of minimising articulation on short-term retention. J. Verb. Learn. Verb. Behav. 10,346-354. Wickelgren, W. A., 1965. Acoustic similarity and intrusion errors in short-term memory. J. Exp. Psychol. 70, 102-108. Wickelgren, W. A., 1966. Phonemic similarity and interference in short-term memory for single letters. J. Exp. Psychol. 71, 396-404.
SHORT
39 (1975), 237-239. Publishing Company.
COMMUNICATION
THE ACOUSTIC
SIMILARITY
EFFECT
Donald MARCER Dept. of Psychology,
Received
January
University of Southampton,
U.K.
1975
The latency of reading 5-word sequences of 3 levels of acoustic similarity was measured. Highly similar sequences were found to have longer latencies than sequences of low similarity or control sequences. The implications of this finding for the acoustic similarity effect in STM are discussed.
It is generally held that verbal material is coded into STM on an acoustic basis. This was demonstrated by Conrad (1962) who showed that errors in the immediate recall of visually presented consonants showed a significant overlap with listening errors for consonants presented in white noise. Similarly Wickelgren (1965) found that errors in the recall of 8-item consonant-letter sequences tended to be of an acoustic nature. Wickelgren (1966) also showed that both RI and PI in STM increase with the phonemic similarity of the interfering material. Baddeley and Dale (1966) have shown that while long-term forgetting of words is related to semantic similarity, it is acoustic similarity that predicts STM loss. Although the acoustic similarity phenomenon has been widely demonstrated, attempts to isolate where in the information processing system (i.e. input, storage or retrieval) the effect occurs have proved less successful. Conrad et al. (1966) were among the first to try to answer this question. They measured the retention of 6-consonant sequences of high or low intra-sequence similarity presented at either 60 or 120 consonants per minute. In all cases the similar sequences showed the worst recall, but there was no rate by similarity interaction. This latter finding led the authors to conclude that the effect was not due to a limitation of the rate at which the encoding system can process
238
II. Marcer /Acoustic
similarity effect
information. However, as correct recall of the similar items in the slow condition was only 18%, it is possible that any interaction was being masked by a ‘floor effect’. In a more detailed investigation Baddeley (1968) again rejected the input deficit hypothesis. He based this conclusion on a finding that STM for word sequences was not attenuated when the level of background noise was increased. Baddeley then presented data which he claimed locates the effect at retrieval. However, whatever the merits of this last claim, Peterson and Johnson (1971) claim that at least part of the effect is dependent on the encoding stage. They found that the superior recall of low-similarity visually-presented messages was eliminated when articulation at input was minimised. Clearly, the extent to which the acoustic similarity effect is located at input is still uncertain. One of the main problems of employing memory experiments to clarify the position is that these effects have to be isolated from those associated with storage or retrieval. The experiment reported here overcame this by measuring how quickly subjects were able to read Sword sequences which differed in their intrasequence acoustic similarity.
Method Using a counterbalanced design 30 Ss read to themselves, as quickly as possible, 15 sequences, each of 5 words. The sequences were of high, low or zero acoustic similarity (HAc, LAc, ZAc). Each sequence was presented as a 5-word unit in a memory drum. The onset of presentation activated a timer which was stopped via a throat microphone when S indicated that he had read the sequence by saying ‘yes’. It was emphasized that, while he must act as quickly as possible, S should be quite sure that he had recognised every word. 3 practice trials were given.
Material Examples of the word sequences are: HAc: tap, pan, fat, fan, pat; LAc: top, pun, pat; ZAc: met, nip, cog, gap, bus. Sequences were matched for word frequency.
fit, fen,
Results The mean latency of responding was HAc = 2.705 set, LAc = 2.375 set and ZAc = 2.382 sec. A repeated measures analysis of variance showed word sequence to be significant at beyond
D. Marcer /Acoustic
similarity effect
239
the 0.1% level (F= 10.60, df 14,406). Scheffe tests showed this to be due entirely to the HAc latency being greater than in the other two conditions which did not differ. In no case was a HAc sequence read more quickly than either a LAc or a ZAc sequence.
Discussion The implications of this experiment can be simply stated. A sequence which is made up of words which are very similar acoustically needs more time to read than one where the items are dissimilar. It follows that if two such sequences are used as stimuli in an STM experiment using visual presentation and equal presentation intervals, then the similar sequence will have less processing time available for each word (according to this experiment about 12% less). This in turn would produce lower levels of learning, with a corresponding lower level of recall, and hence a typical acoustic similarity effect. It remains to be determined to what extent the effect would persist if input levels were equated.
References Baddeley, A. D., 1968. How does acoustic similarity affect short-term memory? Quart. .I. Exp. Psychol. 20,249-264. Baddeley, A. D., H. C. A. Dale, 1966. The effect of semantic similarity on retroactive interference in long- and short-term memory. J. Verb. Learn. Verb. Behav. 5,417-420. Conrad, R., 1962. An association between memory errors and errors due to acoustic masking of speech. Nature 193, 1314-1315. Conrad, R., A. D. Baddeley, A. J. Hull, 1966. Rate of presentation and the acoustic similarity effect in short-term memory. Psychon. Sci. 5, 233-234. Peterson, L. R., S. T. Johnson, 1971. Some effects of minimising articulation on short-term retention. J. Verb. Learn. Verb. Behav. 10,346-354. Wickelgren, W. A., 1965. Acoustic similarity and intrusion errors in short-term memory. J. Exp. Psychol. 70, 102-108. Wickelgren, W. A., 1966. Phonemic similarity and interference in short-term memory for single letters. J. Exp. Psychol. 71, 396-404.