Investigation into acoustic and visual encoding in short-term memory

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.

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.

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

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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 involved the substitution of a similar sounding letter. Based on this research my study aims to investigate whether participants would use acoustic coding in STM even when information is presented visually to them.

Furthermore in a similar study, Conrad demonstrated that participants found it more difficult to recall strings of acoustically similar letters than strings of acoustically dissimilar letters even though they were presented visually. Conrad concluded that such acoustic confusion provided evidence for acoustic coding in STM. Based on the method of this study, it similarity links in with the aim of my study which entails participants would use acoustic coding in STM even when information is presented visually to them.

As seen from the above studies, the investigation aims to look into acoustic and visual encoding in STM. Gaining inspiration from Conrad’s study into acoustic confusion, the researcher will be carrying out a replication of this study, which will look into the effects of acoustic and visual encoding in STM to support his findings. There is a clear distinction that acoustic coding in STM would be used even when information is presented visually, this links into be the experimental hypothesis. Displacement and decay are the theories associated with this research. However the null hypothesis suggests there will be no significance or difference in participants using acoustic coding in STM and when information is presented visually to them. By looking at the experimental hypothesis, it comes to a conclusion that my hypothesis would be one-tailed as it suggests from previous research that coding acoustically is the preferred way. This is supported by Conrad’s study as well as Brandimontes study where images were used instead of words and acoustic coding was preferred over visual therefore indicating the direction of the results.

The following hypotheses have been formed: -

Aim: Investigation into acoustic and visual encoding in STM

Alternative Hypothesis: Acoustic coding in STM would be used even when

information is presented visually.

Null Hypothesis: There will be no significance and difference in participants

recall when using acoustic or visual coding in STM.

The dependent variable in this study will be the type of encoding used in STM, so this will be either the visual or acoustic code used in STM.

The independent variable in this study would be the presentation of visual information.

The extraneous variables would take into consideration the state of mind the participants are in. This can be controlled easily by ensuring the atmosphere and the surroundings of the room have no elements of disturbance within them, which would inevitably affect the short-term memory of participants and lead to subjective results. The level of noise will also be controlled by making sure the room the experiment will take place in, is situated where the level of noise would not highly affect the participants short-term memory. Temperature would be another variable, which would be taken into consideration; this maybe prevented by ensuring the investigation takes place at the same time for all groups of participants. The health of participants may affect their recall if they are experiencing any headaches. Inevitably these variables will have an affect on the dependent variable.

Method

3.1) Design

This study will be similar to Conrad’s study but instead of using acoustically similar and acoustically dissimilar words, these will be replaced by images to make the study somewhat original to Conrad’s work (1964). As the investigation is an experiment the experimental design the researcher will be making use of is repeated measures. This design involves exposing every participant to each of the experimental conditions so in effect participants are used as their own controls. The experiment consists of two conditions, which the participants will be exposed to; these are the acoustically similar images and the acoustically dissimilar images. This experimental design is used as it involves the researcher studying the participants whilst controlling and keeping the extraneous variables consistent. The subject variables may include of individual differences shown by every participant, e.g. intelligence, motivation, past experience etc. These are initially removed as potential confounding variables. Also as there is less variation between conditions, better statistical tests can be used. Moving on fewer subjects are required as data for all conditions is collected from the same group of participants, and as there will be males and females allocated to each group therefore making it more economical. However to reduce order effects, the researcher will consider counterbalancing.

3.2) Participants

The sampling method used in this investigation of visual and acoustic encoding in STM would be opportunistic sampling. This involves the researcher selecting anyone who is available to take part from any given population. This sample might be easily biased or unlikely to be representative of the target population as certain subgroups may not be available for inclusion, however sometimes this is acceptable as research on the capacity of STM reasonably concludes that an opportunity sample of the general public would produce results that did not differ in ways from those obtained from any other kind of sample. The sample will consist of 12 participants. The researcher will possibly control the genders by allocating six participants in one group, but three participants of each gender will be in a group. Inevitably each group of six people will experience both the conditions. The age limit will be controlled, as participants will be selected from a college.

3.3) Apparatus

The apparatus used will include acoustically similar and acoustically dissimilar images prepared by the researcher. (In the appendix) As some of the images maybe hard to interpret due to individual differences the words depicting the images will be displayed onto a screen.

3.4 Procedure

3.4.1 Briefing

As soon as the participants are led to a typical classroom, the researcher will welcome and debrief the participants about the investigation. This will be conducted in the following manner where the researcher will state: “The aim of this experiment is to investigate the effects of acoustic and visual encoding in STM. If you feel the need to withdraw yourself once the investigation has commenced then you have the right to do so. Your confidentiality will be respected and the data produced from this experiment will be destroyed if you do not wish it to be published.” Informed consent of participants will also be gained.

3.4.2 Instructions

The participants that were selected from the population to participate in the investigation were led to a typical classroom. Seating arrangements had an effect as the images were projected in rapid succession onto a screen, so therefore participants were placed in rows to avoid obstacles and the need for them to turn around. As there were two conditions each group experienced the first one followed by the second one.

Standardised procedures were used.

A sheet of lined paper was placed on each desk.
The six female participants were welcomed and seated down in rows.
The images of the acoustically similar words were projected onto a screen for 12 seconds.
Participants were asked to write down the name of the image in the same order as they had appeared on the screen.
The procedure was repeated for the same group, however they had also experienced the second condition, which will be the acoustically dissimilar words.

The precise instructions that were given to the participants by the researcher when they first entered the classroom were: -

“As you all know, an investigation is going to be taking place into the effects of acoustic and visual encoding in STM. Shortly I will be projecting images of acoustically similar and acoustically dissimilar images onto a screen and your task would be to write them down in the order as they appear on the screen.

From as soon as the projection commences onto the screen until the investigation finishes, no communication will be allowed. At any stage of the experiment you have the right to withdraw and your existing data will be destroyed.”

Once the experiment was finished, participants would be asked to leave the room quietly. The paper with the acoustically similar and dissimilar words would be collected and significant errors were noted as well as the number of words each participant recalled.

3.4.3 Debriefing

Once the investigation has finished, participants will be thanked for their participation. The true aims of the experiment were told to the participants before the investigation commenced, so thus the element of deception was not involved. The results/findings collected will also be discussed with the participants and how they found the experience. This would inevitably restore participants to their original state of mind.

Results

Descriptive Statistics

Measures of Central Tendency

Mean: -

Inferential Statistics

The Statistical test that the researcher used was the Sign Test. This is a test of difference that is suitable for use with data gathered from a repeated measures design that are at a nominal level of measurement. The test examines the direction of any difference between pairs of scores.

By viewing the table below, shows the calculations carried out for the Sign Test.

The researcher has chosen this particular statistical test as the investigation predicts a difference between the number of images recalled by each participant. Furthermore there are two conditions in which the experiment will be performed under. This links in with the design being related, as it will involve the same participants being used. The data in the experiment will be non-parametric and will be of the nominal scale as the investigation will involve of 12 participants, which will be allocated into two groups of six with three males and females in each category, experiencing both of the conditions. Counting the frequency of occurrence of the acoustically similar and dissimilar images will determine the number of images recalled by each participant in one of the two groups. The results will then be used to find the difference in their recall.

Discussion

5.1 Explanation of findings:

After calculating the statistical test, I came to a conclusion that I can reject my Null hypothesis and accept my experimental hypothesis, which states that acoustic coding in STM would be used even when information is presented visually. The results obtained from the investigation highlight that fact that acoustic coding is the preferred method of encoding used in short-term memory. This links in with the aim of my experiment, as it was trying to investigate which type of encoding, was mostly used in recall. The descriptive statistics show that there is a trend or some form of acoustic coding involved when participants were trying to recall the acoustically similar images. Which may suggest they are grouping or coding the image in some form of structure in their brain, which inevitably makes recall easier for them. The inferential statistics propose that the obtained results have occurred due to the difference between the sets of scores being so large that it is unlikely to have arisen due to chance, as also my hypothesis was one tailed, indicating the direction of the results. So thereby I can confidently say I have achieved my aim and rejected my null hypothesis.

5.2 The relationship to the background research:

As been inspired by Conrads (1964) study, the replication of his work meant that the researcher could further support his findings by carrying out a replication of his work. However instead of using acoustically similar and dissimilar words, the researcher decided to use acoustically similar and dissimilar images. The results of this investigation go onto similarly support the study conducted by Baddeley (1986) as he clearly found that the similarity of meaning had only a very slight detrimental effect on performance and his conclusion closely matching the conclusion of this research by the short-term memory relying on acoustic coding rather than visual encoding. Interestingly Baddeley tested this with long-term memory and found that the LTM makes use of semantic rather then acoustic coding, which takes place in STM. Moving on, my research findings similarly link in with the conclusions of Brandi Monte’s (1992) study, if the nature of the task is affecting the type of coding used and is 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’s reasonable to conclude that acoustic coding is generally preferred. Therefore, my research should be considered as an extension to prove the statement that ‘acoustic coding in STM is used when information is presented visually’. As clearly many have proved this statement and my research goes onto support these conclusions.

5.3 Limitations and modifications:

By evaluating constructively the method, there are many limitations, which can be modified. The sample size used in this investigation was small to represent a whole population and would have been hard to generalize. This would have led to the results being unrepresentative of the population, which would inevitably lead to the question of unfairness and the results being biased. Using a much larger sample, in order to avoid the question of bias and being unrepresentative of the population would modify this limitation. The study was also limited in the fact that the investigation was only conducted in London, more precisely Walthamstow. This would also be unrepresentative of the population of England and would not apply to everyone. To rectify this, the study can be conducted in each major city of England to represent the population as a whole. Whilst the experiment was taking place, the level of noise in the surroundings was high. This could have led to disturbance and distraction and may have affected the recall of participants. To modify this, the investigation should be conducted in an area where the levels of noise and distraction are not very high, which would lead to fair results.

5.4 Implications and suggestions for further research:

Implications that would arise from my results would lead directly to the society. Carrying out an investigation into acoustic and visual encoding in STM may have changed or enhanced people’s well-being. This has probably led people to perceive society in a different way. Their perceptions of life or the way people think, forget or remember things may have altered. People with forgetful memories, may benefit from using this form of coding in STM, in order for them to improve on their memory and maybe even practice by doing small tasks. Allocating or sampling people with forgetful memories to take part in an experiment, in order to approve or disapprove this idea, can suggest theories or ideas of further research.

The study can also be extended to different age groups, in order to investigate the same effects to suggest further theories or to even different cultures.

Conclusion

By looking closely at the findings of this investigation, it comes to a conclusion that acoustic coding in STM is the preferred method used to code information even when information is presented visually. This clearly links in to be the aim of my investigation, which explores into the two different codes in STM. Thereby rejecting the null hypothesis which states that there will be no difference or significance in participants recall when using acoustic or visual coding in STM and accepting the experimental hypothesis, which highlights the use of acoustic coding over visual encoding.