Bilateral Eye Movement Effect on Incidental Recognition and Source Memory - Essay Example

? Bilateral Eye Movement Effect on Incidental Recognition and Source Memory: A Contradictory Finding to Existing Research Course Professor December 16, 2011 Abstract This study investigated how bilateral eye movements may assist the performance of predominantly right-handed individuals on tasks of incidental recognition and source. Previous research has shown that mixed-handed individuals tend to perform better on these tasks than right-handed individuals, due to increased interhemispheric interaction. It is thought that, moving the eyes back and forth or left and right increases interhemispheric communication (Parker, Relph, & Dagnall, 2008), which in turn should boost performance on incidental recognition and source memory tasks. In the experiment, participants were first determined as mixed-handed or strongly right-handed from Edinburg Handedness Questionnaire. Then they were asked to listen to several word-pairs (e.g. “wet-dry”) and determine whether the words were synonyms or not. This task ensured that the individual deeply processed each word (Christman & Butler, 2011). Following this, they performed a filler task and then eye movements – either up/down or left/right. After this, participants participated in an old/new recognition task. The results showed no significant difference in strongly right-handed individuals after bilateral eye movement for incidental recognition memory or source memory. However, there is an improvement for mixed handed individuals in source memory performance following bilateral eye movement, which contradicts findings by other research. Introduction Why do people have different performance in memory tasks? Apart from the difference in intelligence and age within each individual, one factor that contributes to this performing difference is the way that people use their hands to do tasks. Two types of handedness are common among the population; these are mixed handed and right-handed individuals. Mixed handed individuals use their right hand for many tasks such as writing, but also use their left hand in some situations (e.g. throwing a ball). Right-handed individuals tend to use their right hand for all tasks. Many studies on the effect of handedness and memory showed that mixed handed individuals tend to perform better in some memory tasks, particularly in episodic memory, when compared to right handed individuals. For example, Christman and Butler (2011) found that mixed handed individuals showed superior performance when material is encoded incidentally under conditions which involve deep levels of processing. Another study from Lyle, McCabe and Roediger (2008) also found a mixed handed advantage in source memory tasks. This difference between mixed handedness and right-handedness may be due to the inter-hemispheric interaction. In relation to neuroimaging, it has been found that episodic encoding preferentially activates the left prefrontal region, whereas episodic retrieval preferentially activates the right prefrontal region (Habib, Nyberg, & Tulving, 2003). According to Christman and colleagues (Christman & Propper, 2001; Christman et al., 2003), these results imply that successful episodic memory depends on right hemisphere retrieval processes interacting with memory traces encoded in the left hemisphere. In this way, mixed handed individuals could an advantage in accessing functional process in both hemispheres whereas strongly right-handed individuals may be limited to functional access in left hemisphere. Recent studies on saccade eye movement found that alternating left–right movements are able to increase bihemispheric activation, leading to greater or more efficient hemispheric interaction, which in turn benefits retrieval (Christman, 2003). Complex retrieval tasks such as free recall and difficult recognition tests are thought to depend on hemispheric interaction (Johnson & Raye, 2000) because they simultaneously activate regions in both left and right prefrontal cortex (Nolde, Johnson, & Raye, 1998). Empirically, greater hemispheric interaction has been linked to superior retrieval in comparisons of groups that differ in such interaction. For example, individuals with intact hemispheric commissures show better retrieval than do split-brain patients (Phelps, Hirst, & Gazzaniga, 1991). In addition, the major pathway for interaction—the corpus callosum—is smaller in the strongly right-handed individuals than in the mixed handed individuals (Cowell, Kertesz, & Denenberg, 1993). Therefore, individuals who are strongly right-handed (SR) may experience less hemispheric interaction than individuals who are not (nSR). If eye movements do enhance retrieval by increasing hemispheric interaction (Christman et al., 2003), then the manipulation should differentially affect groups that differ in baseline interaction. A group with less interaction, such as SR individuals, may benefit from eye movements more than a group with greater interaction, like nSR individuals, because members of the former group have a larger margin for increases in interaction. To test this hypothesis, we performed eye-movement manipulations with SR and nSR individuals and tested source memory and incidental old/new recognition. We predicted that bilateral (left/right) eye-movement enhancement on these measures would be greater for SR than for nSR individuals whereas the up/down eye movement control condition would not improve the performance of these individuals on such tasks. Hence, the aim of the study was to examine the interaction between handedness and eye movements and determine how this affects retrieval accuracy. Methods Participants In total 49 young adults (age 17-29) were recruited on a voluntary basis with the incentive of a snack. Participants were friends, family members, and classmates of the investigators in this study. Handedness was established via the Edinburgh Handedness Inventory (EHI; Oldfield, 1971). The median value for the sample on the EHI was 80. Following past practice of studies comparing strong right-handedness to mixed-handedness (e.g. Lyle, Logan, et al., 2008; Lyle, McCabe, et al., 2008; Propper & Christman, 2004; Propper, Christman & Phaneuf., 2005), a median split was performed, dividing the sample into 21 mixed-handers (with EHI scores ranging from -40 to +79) and 23 strong right-handers (EHI scores of +80 or higher). The data for three left-handed participants (EHI scores of -40 or lower) were excluded from analyses. Two further participants were excluded because they did not follow instructions. Informed consent was obtained from all participants. Procedure The study required participants who were either strongly right-handed or mixed-handed. To determine this, participants first filled out Oldfield’s (1971) Edinburgh Handedness Inventory. Once handedness was determined, participants were randomly assigned to either the top/down (control) eye movement condition or left/right (experimental) condition. Participants were then presented with 50 pairs of spoken words (e.g. “wet-dry”), in either a male or a female voice, presented on headphones. Of the 50 word pairs, five pairs in the beginning and another five at the end of the presentation were used as buffers in order to prevent any primary or recency effects. Thus, the recognition test consisted of 80 words, of which half of the words were new and the other half of them were being repeated, all were randomized and counterbalanced between words spoken by female and male voices. The word pairs were simultaneously presented using PowerPoint. The pairs were adapted from Craik and Tulving’s (1975) levels of processing experiment and from Charles’s (2000) experiment on contextual correlates of meaning. For each word pair, the participants were required to decide whether the two words were synonyms and wrote down their responses on a sheet of paper. This procedure was based on Parker, Relph, and Dagnall (2008), who found that presenting word pairs and having participants judge the words required them to associate between the words, thus the words would be deeply encoded. Their study showed this encoding task to be effective concerning bilateral eye movement and handedness. To minimize possible recency effects, participants were given a filler task (a maze) following the word judgment task. Following the filler task, every participant was required to practice eye movements for five seconds facilitated by a PowerPoint presentation. During this presentation, a white dot appeared on a laptop screen against a black background. The dot alternated between the left and right sides of the screen once every 500 milliseconds for 30 seconds. For the control condition, the white dot moved up and down once every 500 milliseconds for 30 seconds. Once the experimenters were satisfied with the participants’ eye movements, the participants were required to perform the eye movements for their respective conditions for 30 seconds. Participants then engaged in a surprise recognition test where they were presented with 80 words and determined whether the presented words were new or had been presented previously. Of the words identified as old, participants were asked to determine whether the word was originally presented in a male or female voice. All answers were recorded on a sheet of paper. Participants then filled out Shipley’s (1940) vocabulary test to help ensure that differences in performance were not due to differences in semantic knowledge. Results Incidental Recognition Participants’ correctly recognized items (hits) and falsely recognized items (false alarms) from the incidental recognition memory task were recorded. Independent variables were handedness and eye movement effect. There was no interaction between eye movement and handedness on incidental recognition memory (Figure 1). Analyses of corrected recognition score showed no significant effect of eye movement (t (42) = 2.02, p = 0.82) nor significant main effect of handedness (t(42) = 2.02, p = 0.32). This result reflected no improvement in incidental recognition from the memory task between control and manipulation conditions. For strongly right-handed participants, there was no significant difference in corrected recognition following left/right eye movement (M = 74.37) or following the control condition (M = 71.87) (t(22) = 2.07, p = 0.68). For mixed handed participants, eye movements (M = 70) produced non-significantly lower corrected recognition than did the control condition (M = 68.75) (t(18) = 2.10, p = .86). This suggested that bilateral eye movement do not improve the performance of incidental recognition test in strongly right-handed or mixed handed individuals. Source Memory The measure of source memory was calculated as the proportion of correctly recognized items that were attributed to the correct source (male or female voice). The scores were then averaged and presented graphically across handedness in each eye movement condition (Figure 2). On this composite measure of source memory and eye movement interacted significantly, (t(42) = 1.68, p =0.049) in the one-tailed t-test, but not in the two-tailed test. Source memory was greater for bilateral eye movement (M = 58.44) than up/down eye movement (control) (M = 52.18). Figure 3 shows the interaction between eye movement and handedness. After experimental manipulation, mixed handed participants did significantly better in source memory recognition when compared to strongly right-handed participants who showed no improvement in performance after the manipulation. For strongly right-handed participants, there was no significant difference in source memory following left/right eye movement (M = 57.00) or following the control condition (M = 55.18) (t(22) = 2.07, p = 0.75). However, for mixed handed participants, eye movements (M = 60.37) produced significantly higher percentage of source memory than did the control condition (M = 49.17) (t(18) = 2.10, p = 0.03). The result suggested that bilateral eye movement improves source memory performance in mixed handed individuals. It is possible that the performance of memory tasks relied solely on sematic knowledge. In order to eliminate this possibility data was examined using a t-test of two-sample assuming equal variances, but there was no significant difference between Shipley score and incidental recognition memory or source memory (Figure 4), although there was a trend towards a better memory as the Shipley score increases. Discussion This study found no significant differences in incidental old/new recognition and source memory for strongly right-handed individuals, which does not support our hypothesis. The finding also does not agree with the results of Christman and Butler (2011), who found the superior performance of mixed handed individuals on a deeper level of processing in incidental recognition task. This deep level of processing, independent of intention to learn, associated with increase activity in the ventrolateral prefrontal cortex, should increase incidental recognition performance in strongly right-handed individuals after bilateral eye movement manipulation. Moreover, our finding is not consistent with that of Lyle, McCabe and Roediger (2008), who suggests that bilateral eye movement improved the performance of strongly right-handed individuals in source memory. One plausible explanation of our findings requires us to revisit the theory of interhemispheric interaction. Bilateral eye movement (left/right) may not improve incidental recognition or source memory. In fact, incidental recognition and source memory may not rely on inter-hemispheric communication at all. Based on the studies of Propper and colleagues, the absence of handedness differences in the recognition memory task is consistent with previous findings that handedness differences in episodic memory are found primarily in recall tasks (Propper et al., 2005), but are typically reduced or absent in recognition tasks. This is thought to occur because strong right-handers can use semantic memory-based feelings of knowing during recognition memory (Propper & Christman, 2004). During recognition, individuals can make two types of judgments regarding their memory for previously presented stimuli: Participants can either “remember” or “know” that they have seen a stimulus previously. One interpretation of such differences in memory judgment types is that “remembering” involves the recollection of specific aspects of an event, and is an episodic memory for a previously presented stimulus. In contrast, “knowing” does not require the recollection of specific features of a stimulus, and is analogous to having a semantic representation of an item (Diana et al. 2006). It is possible that we found no improvement after bilateral eye movement in strongly right-handed individuals for incidental recognition test was because our participants depended on unihemisperically mediated rather than bihemispherically mediated sematic memory. Furthermore, studies on patients suggest that the ability to recognize previously studied words might not depend on hemispheric interaction. For example, two callosotomy patients in Phelps et al. (1991) made old/new recognition judgments about words as accurately as did age- and education-matched controls. This is consistent with the notion that hemispheric interaction is, if not wholly unimportant for recognition, substantially less important for recognition than for free recall. In addition, the implicit state of the recognition test may play a part in producing the results we obtain. Christman, Propper, and colleagues have found that implicit test of fragment completion (Propper et al., 2005) is not dependent on hemispheric interaction. Hemispheric interaction via the forebrain commissures is not necessary for implicit completion of word fragments with previously studied words, because patients with complete callosotomies show normal priming effects on fragment completion tasks (Kroll et al., 2003). Note, however that fragment completion may depend on the interhemispheric transfer of information via subcortical routes (Cronin-Golomb et al., 1996). This may explain why we found no improvement on the performance of strongly right-handed individuals in incidental old/new recognition task. However, for deeply encoded words or “remember” words in our source memory task should have found an interaction with bilateral eye movement for strongly right-handed individuals according to many existing studies (e.g., Christman et al., 2003; Lyle, McCabe, & Roediger, 2008; Lyle, Logan, & Roediger, 2008). Despite many studies supporting interhemisteric interaction for source memory retrieval, we found no improvement in source memory after bilateral eye movement for strongly right-handed individuals. In fact, we found the improvement of mixed handed individuals on source memory after the experimental manipulation. This finding contradicts findings from scientific literature, and as a consequence, limitations in our study that may have influence our results. One major limitation to our study is the small sample size, especially in mixed handed group where there were a total of eight participants in the control condition and 13 participants in experimental condition. With almost half the number of experimental condition people in control condition, it may be due to chance that participants in experimental condition have higher source memory score when compare to the control condition. Similarly, the fact that there is no improvement across conditions for strongly right-handed individuals may be due to the limiting number of participants. If we were to have more participants who were mixed handed, finding an effect of bilateral eye movement on source memory may have been likely. Another limitation is the participants we recruited. Because most of the participants were friends, many of the subjects may not have been serious when they were completing the required tasks. In addition, this method of selection leads to bias in sampling and could have an effect on the outcome of the experiment. Some tasks needed a substantial amount of attention such as the listening task because some spoken word pairs were quite difficult to understand and individuals could only listen to each pair once. There were also some noises during the experiments, which could have reduced the participants’ attention to the tasks. Further research is needed in order to clarify if the results of this study are important to the scientific community or if they are due to confounding factors. More participants are needed in the future research and the experimental design should be improved. For example, all participants should be using only one computer while doing the tasks and the programs needed for experiment like voice generator should be a good one that can generate clear distinctive voice. Ultimately, this study can use some improvements before we can get convincing results. References Charles, W. G. (2000). Contextual correlates of meaning. Applied Psycholinguistics, 21, 505-524. Christman, Stephen D., & Butler, M. (2011). Mixed-handedness advantages in episodic memory obtained under conditions of intentional learning extend to incidental learning. Brain and Cognition, 77(1), 17-22. Christman, S. D., Garvey, K. J., Propper, R. E., & Phaneuf, K. A. (2003). 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Memory & Cognition, 33, 751–757. Shipley, W. C. (1940). A self-administering scale for measuring intellectual impairment and deterioration. Journal of Psychology: Interdisciplinary and Applied, 9, 371-377. Figures Figure 1: Mean corrected recognition score as a function of handedness and eye movement. Figure 2: Mean source memory score across handedness in each condition Figure 3: Mean source memory score as a function of handedness and eye movement. Figure 4: Mean Shipley score across handedness in each condition Read More