Investigation into acoustic and visual encoding in short-term memory

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Investigation into acoustic and visual encoding in short-term memory

  1. Abstract


The investigation aims to look into acoustic and visual encoding in short-term memory (STM). The research associated with this experiment is supported by Conrad’s (1964) study into acoustic confusion. The experimental hypothesis was tested and led the researcher to accept it, as it stated that acoustic coding in STM would be used even when information is presented visually whereas the Null hypothesis was due to chance alone and predicted that there will be no significance or difference in participants recall when using acoustic or visual coding in STM.

 Repeated measures was the design used for this investigation, as it involved exposing every participant to each of the experimental conditions, so in effect participants were used as their own controls.

        Opportunistic sampling was used to select participants to take part in this investigation. The findings of this investigation direct us towards accepting the experimental hypothesis that a vast number of people would use acoustic coding in STM. The statistical test used was the Sign Test as the statistical significance was 0.05% of the results with a critical value of one, which clearly suggested that the experimental hypothesis could be accepted, as the hypothesis was one tailed leading to reject the null hypothesis. The conclusions drawn from this study highlight that most people use acoustic coding over visual coding.

  1. Introduction


The investigation will be focusing on visual and acoustic coding in short-term memory (STM). According to acoustic and visual encoding in STM the capacity of STM is limited to approximately seven chunks of information as suggested by Miller (1956). A study by Brandimonte (1992) into visual encoding in STM demonstrated that not only visual coding can be used in STM but also that under certain circumstances it is a superior method. Participants were presented with six drawings of familiar objects and asked to memorize them. They had to form a mental image of each one and subtract a specified part of the drawing and name the resulting image. Another group were asked to do the same except they were prevented from articulating during the learning stage. They were asked to repeat a meaningless chant. This prevented them form converting the pictorial image into a verbal code. They were more successful in identifying the subtracted image as they were using visual coding. This study links in with the aims of my investigation as the nature of the task may affect the type of coding used and if prevented from using acoustic coding, visual coding maybe substituted showing evidence that items in STM can be coded in terms of their meaning so it seems reasonably to conclude that acoustic coding is preferred.

The theory associated with this research is displacement as this maybe a possible mechanism for forgetting from STM. According to this theory material currently circulating in STM, which has been insufficiently processed to pass onto LTM, will be pushed out or displaced by new incoming information. However displacement is not the only theory associated with this research, according to the decay theory information is forgotten due to the passage of time. It is thought that some kind of structural change occurs in the brain when a memory is laid down. Hebb (1949) believed that as a result of excitation of the nerve cells a brief memory trace is laid down. At this precise stage of the process, which corresponds to STM, the trace is very fragile and likely to be disrupted. However, with repeated neural activity  (e.g. brought about by rehearsal) a permanent structural change comes about and the memory is transferred to LTM where it is no longer likely to decay.

One study, which looked into the displacement theory, was carried out by Waugh and

Norman (1965) using the serial probe technique. The investigation commenced by the presentation of a set of digits followed by the repetition of one of those digits (the probe). This was followed on by participants recalling the digit that followed the probe in the original list. Recall was good if the probe came towards the end of the 16-digit list but poor for items at the beginning of the list. This study is consistent with the notion of displacement as the digits at the end of the list would still be available in STM whereas digits at the beginning of the list would seem to have been displaced by the ones that came later.

Moving on, the effects of acoustic similarity using words than letters was explored by Baddeley (1986). Participants were presented with sequences of five short words taken from a pool of words, which were acoustically similar. Baddeley compared their serial recall performance with that of sequences of short acoustically dissimilar words and sequences of short semantically similar words. Like Conrad, Baddeley equally found that words with similar sounds were much harder to recall than words that did not sound alike. Similarity of meaning had only a very slight detrimental effect on performance. Baddeley concluded that STM relies on acoustic coding. Interestingly he found that the effects of sound similarity disappeared when he tested participant’s long-term memory. He extended the length of the word lists from five to ten and prevented participants from repeating the words by interrupting them after each presentation. The lists were presented four times and recall was tested after 20 minutes. Under these conditions, participants found recall of the semantically similar words much more difficult then recall of the acoustically similar words. In conclusion, Baddeley stated that long-term memory makes use of semantic rather than acoustic coding.

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        One other study that looked into the notion of acoustic confusion was carried out by

Conrad (1964). The aim of the investigation was to find out whether people would use

acoustic coding in STM even when information is presented visually to them. The investigation began by participants being shown random sequences of 6 letters. These letters were shown in rapid succession on a screen and participants were required to write them down. As the rate of presentation was too fast, they had to rely on their memory. Conrad carefully noted the errors and found that the significant majority ...

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