Running head: DIGITS, LETTERS, AND WORDS ON MEMORY SPAN 2
DIGITS, LETTERS, AND WORDS ON MEMORY SPAN 2
The Influence of Digits, Letters, and Words
Abstract
A memory span experiment was carried out among 129 students studying at Murdoch University in Singapore to determine the relationship between stimulus type (digits, letters and words) and memory span, which was defined as the length of the last list the subject correctly recalls. The 129 participants were asked to recall lists of digits, letters, and words, and had their number of items recalled recorded. Results indicated that there is a significant difference between the stimulus type and the length of last list recalled. Subjects tested recalled a longer list of items for the stimulus type digits (M= 6.53, SD = 1.31) as compared to the stimulus type letters (M= 5.71, SD= 1.34) and the stimulus type words (M= 4.17, SD= 1.07). The difference recorded is significant for all three-stimulus type. Further research is needed to clarify whether one’s memory span is the best when it comes to the stimulus type digits, and whether there is other stimulus which affects memory span.
The Influence of Digits, Letters, and Words on Memory Span
This research will cover the impact of three different stimulus types on memory span, and to find the stimulus type with the greatest effect, if possible. To break it down, memory span is a measure of working memory or short-term memory (STM) capacity. According to Gary & Bill (2015), STM is an aspect of long-term memory (LTM) that is used or activated by limited capacity attentional process. Similarly, working memory (WM) is also an important cognitive function which is critical for spontaneous and active behaviour (Wolff, Jochim, Akyurek, & Strokes, 2017). For this research, STM and WM will be used interchangeably. There is no standard limit or number for memory span capacity in general, however past researches have assessed the span limit to be about seven, with a leeway of plus and minus two (Bachelder & Delprato, 2017). The three different stimulus types here – digits, letters, and words – are categories of items in which result in different processing methods, hence different number of recalled items. These stimuli are randomly presented, without the inference from other stimulus. The stimulus type digits, is deemed to be the easiest stimulus when it comes to memory span capacity.
According to a study Altani, Protopapas, & Georgiou (2017), three cognitive processes are linked to ‘memorizing’ or ‘trying to recall’ something during which the stimuli are presented. The first process is known as shifting, where one disengages from the previous stimulus and rapidly engages on the next stimulus. The second process is known as inhibition, where one suppresses the focus on the previously activated stimulus and refocuses on the activation of the next stimulus. The third process is known as updating, where one observes and monitors the current visual stimulus and registers in it the phonological representation in one’s working memory. The process of inhibition is significantly related to letters and digits, which indicates that digits and letters are ‘easier’ to be recalled – absorbing the input into the sensory memory, storing it in the STM, rehearsing it, and retrieved when needed. (Atkinson & Shiffrin, 1968).
It has been found that the WM has a limited capacity which is used for temporary storage of information. Because this experiment conducted is a simple span task, with no irrelevant stimuli involved to distract the subject from the current stimuli, it makes it easier to find the visual stimulus type that has the greatest influence on the subject, allowing the recall of that category of items to be easier. Another study by Egeland (2015), which measured working memory span with digit span task and the letter-number sequencing subtests from the Wechsler Adult Intelligence Scale (WAIS) IV, found that participants scored better on the digit span task as compared to the letter-number sequencing subtests. However, this could partly be because the number sequencing subtests require the manipulation of information for the participants, and that two different stimuli were introduced into the test – letters and numbers.
Katrine et al. (2017) did an experiment on 1,145 children, to compare their executive functions, physical activity and academic performance. A small part of the experiment included the children doing the Digit Span Task, which involved the reciting and recalling of the digits after the set of numbers is relayed to the child. This led to a finding of the high numeracy recall in both genders. It has been found that although there are age differences which affect working memory, in general, people are more sensitive towards numbers, as compared to letters, which form words. It is common to have people memorize their phone numbers, identification card numbers, and a 16-digits long set of numbers imprinted on credit or debit cards. Though the method of chunking helps with the memorizing of numbers, it does work with letters or words too. Memorizing numbers in a certain fixed sequence is more commonly practiced than memorizing letters or words. Hence, the memory span for digits tend to always be higher than letters and words.
However, there were also studies that argued that there is no significant difference between stimulus type and memory span. Many of which suggests that differential distinctiveness and rehearsal time, affects the working memory span more than than the visual or auditory stimulus type that is used.
The present study aimed to determine whether the working memory capacity is stimulus type specific. More specifically, the stimulus type digits would render a better or higher working memory capacity, as compared to the stimulus type letters and words. From the research examined, it was hypothesized and anticipated that the 129 participants would be able to recall a longer list of items when they were in digits, slowly shorter list of items when they were in letters, and even shorter list of items when they were in words. The independent variable here would be the length of the last list that was recalled by the subject, while the dependent variable would be the stimulus type – digits, letters and words.
Method
Participants
The 129 participants in this study consisted of undergraduate psychology students from Murdoch University in Singapore. Sixty-four males and sixty-five females, who were between eighteen and thirty years of age (M = 24.27) were involved in this study. The sample was predominantly in the mid-class. All the participants were Singaporeans, and participation by the students was encouraged but voluntary, with no incentives offered. Ethic approval was attained from the Singapore Psychological Society (SPS) under 2019/123.
Materials
There were three categories of tests which were used – digits, letters and words. 8 sets of the different categories were pre-prepared, in ascending number of items in the set, starting from three. All the digits, letters and words in the list were all in random order, and different for each of the 129 participants. The list of digits, letters and words were printed in bold and capital letters. The scores for the length of list recalled range between three to ten. Higher scores indicated more digits, letters or words recalled, while lower scores of below five were indicative of below-average working memory capacity. This method of testing the subjects with the visual stimulus, with no irrelevant distractions, allows the subjects to focus and recite the items when needed.
A demographic data sheet that asked for information such as gender, age, and socioeconomic state was also included.
Procedure
All 129 participants were tested individually, concurrently. The subject starts with the digits task first – where the first list of three items were presented. The subject then recalls the three digits shown. If correctly recalled, the list increased to four digits and so on till the longest list of ten digits. At any point where the subject failed to recall the list of digits, the length of the last list correctly recalled will be the memory span for that particular stimulus type. This was repeated for the stimulus type letters and words, and the length of the last list correctly recalled was recorded. All 129 subjects went through three rounds of different stimulus types.
Instructions for the task were relayed to each subject specifically. Each subject had 15 seconds to do their task on each list of stimulus type. If the subject fails to complete the recall, it would be taken as the list of items at that point would be incorrect. Each participant’s data was kept anonymous and pooled together after the experiment. The scores were then recorded and analyzed using the Statistical Package for Social Scientists (SPSS, standard version 6.1.2, 1995).
Results
A repeated measures analysis of variance (ANOVA) was used to compare the effects of the three stimulus types on the length of the last list recalled by the subject. The independent variable here is the length of the last list recalled by the subject for that particular stimulus type, and the dependent variables include the three different stimulus types – digits, letters, and words. All stimulus types were statistically significant at the .05 significance level. Shapiro-Wilk and Levene’s tests were used to evaluate the assumption of normality and homogeneity of variance respectively. Neither was violated. The Bonferroni test was used to ensure that adjustments were made for multiple pairwise comparisons.
The ANOVA revealed a statistically significant difference for all three stimulus types, at p < .05. The means and standard deviations for the stimulus type digits, letters, and words, were 6.53 and 1.31, 5.71 and 1.34, and 4.17 and 1.07, respectively.
Discussion
The results, showing that there is a significant difference between stimulus types and the length of the last list recalled, and that the stimulus type of digits rendered the highest number of items recalled, is as expected. This is in accordance to the hypothesis proposed and has also been consistent with the findings of many other researches.
Comparing the different stimulus types presented in this study, it seems that the participants tend to recall more items, when it comes to digits. This finding is in accordance with a study by Milikowski & Elshout (1995) who found that it is easier to remember a digit as compared to a letter or word. This finding thus supports our hypothesis that the length of the last list recalled for digits is higher than that of letters and words.
Additionally, although Miller (1956) have suggested that the working memory is limited to five to nine items, the data recorded for the participants under digits did exceed that special number of seven plus minus two, with three participants recalling the maximum of 10 digits. This is in comparison to the maximum record of nine and eight for letters and words, respectively.
A limitation of the study would be that the 129 participants were not previously medically screened to ensure that they had no cognitive issues or problems that could have affected the results recorded. Pre-tests should have been done on the participants, to ensure that cognitively, they were on the same level. This is because cognitive or developmental conditions such as dyslexia and language impairment, which affects the reading and learning capabilities of one, can affect the results recorded (Archibald and Gathercole, 2006).
Another confounding variable that can tamper with the results recorded, would be that as working memory can be affected or impaired when one is stressed (Preuss & Wolf, 2008), the wellbeing or state of mind of the participants in the study, was not taken into consideration. The study, if conducted during stressful examination periods, can affect the participants cognitively, and cause the results recorded to be inaccurate and invalid.
Overall, the results of the study suggest that the stimulus types do have an effect on working memory capacity. There are many past researches which found digits or numbers, tend to be easier to be memorized and retrieved when needed. It has also been found that letters and words require more effort when it comes to inhibiting it into one’s mental dictionary. However, the underlying factors remain largely unexamined, and it would be a good direction for future researchers to work why certain stimulus may be easier to be ingrained in our minds, and why are some information lost so easily. Further research could include other methodologies which can pinpoint the exact differences in the stimulus types, and thus help in improving learning opportunities for the young and old.
References
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