Why does saccade execution increase episodic memory retrieval? A test of the top-down attentional control hypothesis

Differences Between Consistent and Inconsistent Handedness Remain Consistently Interesting: Ten Years of Research on the Consistency of Handedness With the Edinburgh Handedness Inventory

Almost 10 years ago Prichard et al. (2013) published a literature review on consistency of handedness. They described how consistency of handedness, typically measured by the Edinburgh Handedness Inventory (EHI), predicted outcomes in memory and decision-making paradigms better than direction of handedness. In the last 10 years, new research has extended these findings and added new theoretical perspectives. The goal of this short form review is to highlight and summarize some of these more intriguing findings and to encourage researchers in the fields of memory and decision making to incorporate handedness as a variable in future research.

Effects of saccadic eye movements on episodic & semantic memory fluency in older and younger participants

Research has demonstrated that performing a sequence of saccadic horizontal eye movements prior to retrieval facilitates performance on tests of episodic memory. This has been observed in both laboratory tasks of retention and autobiographical memory. To date, the work has centred on performance in younger individuals. This paper extends previous investigations by examining the effects of saccadic eye movements in older persons. Autobiographical episodic and semantic memory fluency was assessed in younger (age range 18-35, mean = 22.50), and older (age range 55-87, mean = 70.35) participants following saccadic (vs. fixation control) manipulations. The main effects of eye movements and age were found for episodic autobiographical memory (greater fluency after eye movements and in younger participants). Semantic autobiographical memory showed a main effect of age (greater fluency in younger participants), whereas general semantic memory showed no effect of age or eye movement. These findings indicate that saccadic horizontal eye movements can enhance episodic personal memory in older individuals. This has implications as a technique to improve autobiographical recollection in the elderly and as an adjunct in reminiscence therapy.

Memory Effects of Manipulating Text Column Width: Eye-Movement Induced Attentional Processes Interfere With Prose Encoding Among Consistent Handers

Performing bilateral saccadic eye-movements has enhanced subsequent verbal recall among consistent handers (people who use their dominant hands for virtually all tasks) but not inconsistent handers (people who use their non-dominant hands for some tasks); but eye-movements prior to encoding have disrupted recall in consistent handers. We sought to better understand how this research might be applied to recalling written text presented in ways that differentially affected eye movements. We manipulated text column width in order to test whether induced eye movements and resultant right hemisphere activations would lead consistent handed (versus inconsistent handed) readers to experience encoding disruptions and poorer recall of the written passage. We presented participants, divided by handedness consistency and gender, with a story about a fictional island in which the lines of text were either ∼28 or ∼120 characters wide. We later asked participants to answer 20 questions about the story and measured their memory performance by both their percentage of correct answers and by their correct answers adjusted for a guessing tendency. We found a handedness by text width interaction. Consistent handers who read the story in a narrower column width showed poorer recall than both inconsistent handers and consistent handers who read the story in the wider text column. We suggest a chain of events such that text width altered eye-movements that, in turn, activated right hemisphere brain processes associated with orienting attention and attentional control, competing with consistent handers' encoding.

The electrophysiological underpinnings of variation in verbal working memory capacity

Working memory (WM) consists of short-term storage and executive components. We studied cortical oscillatory correlates of these two components in a large sample of 156 participants to assess separately the contribution of them to individual differences in WM. The participants were presented with WM tasks of above-average complexity. Some of the tasks required only storage in WM, others required storage and mental manipulations. Our data indicate a close relationship between frontal midline theta, central beta activity and the executive components of WM. The oscillatory counterparts of the executive components were associated with individual differences in verbal WM performance. In contrast, alpha activity was not related to the individual differences. The results demonstrate that executive components of WM, rather than short-term storage capacity, play the decisive role in individual WM capacity limits.

Re-evaluating whether bilateral eye movements influence memory retrieval

Several recent studies have reported enhanced memory when retrieval is preceded by repetitive horizontal eye movements, relative to vertical or no eye movements. The reported memory boost has been referred to as the Saccade-Induced Retrieval Enhancement (SIRE) effect. Across two experiments, memory performance was compared following repetitive horizontal or vertical eye movements, as well as following a control condition of no eye movements. In Experiment 1, we conceptually replicated Christman and colleagues’ seminal study, finding a statistically significant SIRE effect, albeit with weak Bayesian evidence. We therefore sought to conduct another close extension. In Experiment 2, horizontal and vertical eye movement conditions were manipulated separately, and sample size was increased. No evidence of a SIRE effect was found: Bayesian statistical analyses demonstrated significant evidence for a null effect. Taken together, these experiments suggest that the SIRE effect is inconsistent. The current experiments call into question the generalizability of the SIRE effect and suggest that its presence is very sensitive to experimental design. Future work should further assess the robustness of the effect before exploring related theories or underlying mechanisms.

Saccade-induced retrieval enhancement and the recovery of perceptual item-specific information

Saccade-induced retrieval enhancement (SIRE) effects refer to the finding that memory can be enhanced when a short period of saccadic eye movements takes place prior to retrieval. Previous published work testifies to this eye movement advantage, but no work has yet examined if SIRE effects can be found when retrieval demands are high as a result of testing non-studied memoranda that are identical in name/conceptual codes, similar in perceptual features, but differ in terms of perceptual-item-specific information. The results indicate SIRE effects can be found under such conditions and are independent of encoding orientation (intentional vs. incidental). More particularly, SIRE effects manifested themselves in terms of the retrieval of item-specific detail and recollection (vs. familiarity). In terms of the latter, recollection but not familiarity was enhanced by eye movements. These findings are considered in the context of extant theories of SIRE and related research.

Should we pay attention to eye movements? The impact of bilateral eye movements on behavioral and neural responses during the Attention Network Test

Bilateral eye movements (EMs) have been associated with enhancements in episodic memory and creativity. We explored the influence of EMs on behavior and event related potential (ERP) responses during the Attention Network Test (ANT). Participants completed ANT trials after bilateral EMs or a center-fixation control manipulation. We examined condition (EM, control) and handedness (consistent, inconsistent) differences for overall task performance, as well as alerting, orienting, and executive attention networks. Behaviorally, there was a trend for inconsistent-handed participants to display faster RTs across cue types, and greater accuracy for no cue, double, and center cue trials when compared to consistent handers, yet consistent handers garnered greater improvements in behavior following altering and orienting cues than inconsistent handers. Although there were no behavioral differences between EM and control conditions, target-locked N100 and P200 ERPs were weaker in the EM than control condition for all cue types, except spatial cues for which there were no differences between groups. Because stronger N100 and P200 responses have been linked to increased selective attention, we speculate that ERP differences between EM and control conditions, in the absence of behavioral differences, may indicate that participants exposed to EMs required less selective attention to successfully complete the task.

Saccades and handedness interact to affect scene memory

Repetitive saccades benefit memory when executed before retrieval, with greatest effects for episodic memory in consistent-handers. Questions remain including how saccades affect scene memory, an important visual component of episodic memory. The present study tested how repetitive saccades affect working and recognition memory for novel scenes. Handedness direction (left–right) and degree (strong/consistent vs. mixed/inconsistent) was measured by raw and absolute laterality quotients respectively from an 8-question handedness inventory completed by 111 adults. Each then performed either 30 s of repetitive horizontal saccades or fixation before or after tasks of scene working memory and scene recognition. Regression with criterion variables of overall percent correct accuracy and d-prime sensitivity showed that when saccades were made before working memory, there was better overall accuracy as a function of increased direction but not degree of handedness. Subjects who made saccades before working memory also performed worse during subsequent recognition memory, while subjects who fixated or made saccades after the working memory task performed better. Saccades made before recognition resulted in recognition accuracy that was better (Cohen’s d = 0.3729), but not significantly different from fixation before recognition. The results demonstrate saccades and handedness interact to affect scene memory with larger effects on encoding than recognition. Saccades before scene encoding in working memory are detrimental to short- and long-term memory, especially for those who are not consistently right-handed, while saccade execution before scene recognition does not appear to benefit recognition accuracy. The findings are discussed with respect to theories of interhemispheric interaction and control of visuospatial attention.

Interhemispheric Activation and Memory Function: Considerations and Recommendations in the Context of Cardiovascular Exercise Research

The field of neurobiology of learning and memory has demonstrated that interhemispheric activation plays an important role in subserving episodic memory function. A common behavioral technique to induce interhemispheric activation includes saccadic eye movements, with a common behavioral marker being the degree of handedness. Importantly, however, the field of exercise neurobiology has yet to consider these behavioral techniques and markers in exercise-based studies. This review highlights the effects of these techniques and markers on episodic memory function and discusses the implications of this for exercise studies. We discuss the physiological and neurological mechanisms of interhemispheric activation on memory. We also discuss the role this may play in cardiorespiratory exercise studies. Our understanding of the role of both exercise and interhemispheric activation on memory function is improving. The interplay between these two factors on memory, however, is unknown. We discuss these implications and provide recommendations for future research.

Changes in brain connectivity following exposure to bilateral eye movements

The present research assessed how engaging in bilateral eye movements influences brain activity. Participants had their resting-state brain activity recorded with electroencephalography (EEG) before and after they performed 30 s of bilateral eye movements or a center-control manipulation. We assessed differences in change scores for absolute power and coherence between the eye-movement and center-control conditions. A main effect for handedness was present for EEG power in the theta and beta frequency bands, with inconsistent-handed participants displaying a greater increase than consistent-handed participants in both frequency bands. For theta, the increase in power for inconsistent handers was specific to participants in the bilateral eye-movement condition, whose increase in theta power exceeded the increase in theta power for consistent-handed participants regardless of condition. In contrast, for coherence, a main effect for condition was present for the delta frequency band, with participants in the control condition exhibiting a significant drop in posterior delta coherence pre to post. We suggest that the maintenance of posterior delta coherence over time may be an important factor in sustaining attention. Further, the malleability of EEG power for inconsistent-handed participants reveals the importance of individual-differences variables in the potential for behavioral manipulations to change brain activity.

Effects of handedness consistency and saccade execution on eyewitness memory in cued- and free-recall procedures

Identifying characteristics that distinguish between people with relatively good versus poor episodic memory is an important goal of eyewitness-memory research, as is identifying activities that can improve people's ability to retrieve episodic memories. Consistency of hand preference is a trait associated with the quality of people's episodic memory and repetitive saccade execution is an activity known to improve people's ability to retrieve episodic memories. These factors were examined in relation to cued and free recall of a staged criminal event. Individuals with inconsistent hand preference (versus consistent) remembered more on a cued-recall test and also freely recalled a larger amount of victim information. Repetitive saccade execution did not increase cued recall but did increase free recall of victim information. Theoretical implications are discussed, as is potential practical significance, with an emphasis on the size of the observed effects.

Effects of Saccade Induced Retrieval Enhancement on conceptual and perceptual tests of explicit & implicit memory

The effects of saccadic horizontal (bilateral) eye movements upon tests of both conceptual and perceptual forms of explicit and implicit memory were investigated. Participants studied a list of words and were then assigned to one of four test conditions: conceptual explicit, conceptual implicit, perceptual explicit, or perceptual implicit. Conceptual tests comprised category labels with either explicit instructions to recall corresponding examples from the study phase (category-cued recall), or implicit instructions to generate any corresponding examples that spontaneously came to mind (category-exemplar generation). Perceptual tests comprised of word-fragments with either explicit instructions to complete these with study items (word-fragment-cued recall), or implicit instructions to complete each fragment with the first word that simply 'popped to mind' (word-fragment completion). Just prior to retrieval, participants were required to engage in 30 s of bilateral vs. no eye movements. Results revealed that saccadic horizontal eye movements enhanced performance in only the conceptual explicit condition, indicating that Saccade-Induced Retrieval Enhancement is a joint function of conceptual and explicit retrieval mechanisms. Findings are discussed from both a cognitive and neuropsychological perspective, in terms of their potential functional and neural underpinnings.

The effects of varying levels of hemispheric activation on episodic memory

Bilateral saccadic eye movements enhance episodic memory retrieval; however, this usually only occurs for consistent-handed, not inconsistent-handed, individuals. It was hypothesized that inconsistent-handers begin closer to the peak of a Yerkes-Dodson-type inverted-U curve and increasing activation pushes them along the curve eventually decreasing performance, while consistent-handers start at a lower baseline and therefore increasing activation increases their performance. The current study tested this hypothesis by using hand clenching (grip strength) to increase activation at 5 different levels for both consistent- and inconsistent-handers. A total of 316 participants were presented with a list of 36 words after which they squeezed a hand dynamometer to induce cortical activation, and then recalled as many of the words as they could. Results showed that, as predicted, both inconsistent- and consistent-handers demonstrated an inverted-U pattern of memory performance as the strength of squeeze increased with inconsistent-handers peaking at a lower level of grip strength than consistent-handers. These results may help explain past findings, not only with episodic memory but also a variety of other cognitive tasks. They may also have interesting theoretical and real-world implications, which are discussed.

Replication Requires Psychological Rather than Statistical Hypotheses: The Case of Eye Movements Enhancing Word Recollection

Can an experiment be replicated in a mechanical fashion without considering the processes underlying the initial results? Here I will consider a non-replication of Saccade Induced Retrieval Enhancement (SIRE) and argue that it results from focusing on statistical instead of on substantive process hypotheses. Particularly the theoretical integration of SIRE with Eye-Movement Desensitization and Reprocessing (EMDR) therapy, provides clues about when the memory enhancement should occur. A relatively large memory enhancement effect in participants with a consistent (i.e., extreme right or left) handedness should be observed, (a) when explicitly instructed to retrieve and imagine the memories during the eye manipulation, and (b) for emotionally negative material. A finer theoretical analysis may thus well explain the contrast between the original SIRE studies and the non-replication. Also the findings from preregistered confirmatory research (i.e., focusing solely on statistical hypotheses) should be considered preliminary, representing shifts on a gradual scale of evidence, and awaiting interpretation in terms of theoretical hypotheses. Stronger, but still not definitive, conclusions can better be postponed until after multi-study meta-analyses with theoretically motivated moderator variables have been performed.

Relationship between sustained unilateral hand clench, emotional state, line bisection performance, and prefrontal cortical activity: A functional near-infrared spectroscopy study

Sustained unilateral hand clenching alters perceptual processing and affective/motivational state, with these alterations presumed to reflect increased hemispheric activity contralateral to the side of motor movement. However, data from electroencephalographic and imaging studies are contradictory regarding the relationship between sustained hand clenching and brain activity. In order to investigate the relationship between brain activity, sustained unilateral hand clenching, and changes in affect and perceptual processing, frontal hemispheric activity was measured via functional near-infrared spectroscopy (fNIRS), using derived O₂Hb prior to, during, and post-sustained unilateral hand clench. Participants' mood and spatial perception were recorded pre- and post-clenching. Sustained unilateral hand clenching altered brain activity and mood, but not spatial perception. Results revealed increased O₂Hb bilaterally following sustained unilateral hand clenching, relative to baseline, regardless of hand. In agreement with previous fNIRS studies, sustained unilateral hand clenching resulted in greater ipsilateral, compared with contralateral, O₂Hb. An interaction between side of hand clench and change in mood was in the direction predicted by theories of hemispheric lateralization of emotion: Following left-hand clenching, individuals became more affectively negative, and following right-hand clenching, they became more affectively positive.