Inconsistent handedness and saccade execution benefit face memory without affecting interhemispheric interaction

Individuals who consistently use their dominant hand for most tasks exhibit poorer memory than individuals whose handedness is relatively inconsistent, but consistent-handers’ memory can be enhanced by making repetitive saccadic eye movements before attempting retrieval. One account of these effects is that inconsistent handedness and saccade execution are associated with increased interhemispheric interaction, which putatively facilitates retrieval. We tested this account by having participants classify faces as famous or novel. Faces were presented in the left and right visual fields simultaneously (bilaterally) or in one field only (unilaterally). As in prior studies, famous faces were classified more quickly and more accurately given bilateral presentation, but novel faces were not. These bilateral gain effects indicate that interhemispheric interaction specifically facilitates famous-face recognition, and therefore larger gains may reflect greater interhemispheric interaction. However, neither inconsistent handedness nor saccade execution increased the size of bilateral gain. Inconsistent handedness and saccade execution (the latter for consistent-handers only) did increase face-classification accuracy, but the increases were not specific to famous-face recognition, and, in fact, were somewhat stronger for novel-face identification. These results extend the beneficial mnemonic effects of inconsistent handedness and saccade execution to faces, but indicate that these benefits are not caused by increased interhemispheric interaction.     

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.     

Individual differences in risk perception versus risk taking: handedness and interhemispheric interaction

Research indicates that right-hemisphere mechanisms are specifically sensitive to and averse to risk. Research also indicates that mixed degree of handedness is associated with increased access to right hemisphere processing. Accordingly, it was predicted that mixed-handers would exhibit greater risk aversion. Participants were presented with various risky activities and were asked to rate (i) the perceived risk, (ii) the perceived benefit, and (iii) their likelihood to engage in each activity. No handedness differences were found for any of these ratings. Regression analyses, however, indicated that the likelihood to engage in risky activities was predicted primarily by the perceived risks in mixed-handers and by the perceived benefits in strong-handers.     

Bimanual coordination and interhemispheric interaction

Bimanual coordination of skilled finger movements requires intense functional coupling of the motor areas of both cerebral hemispheres. This coupling can be measured non-invasively in humans with task-related coherence analysis of multi-channel surface electroencephalography. Since bimanual coordination is a high-level capability that virtually always requires training, this review is focused on changes of interhemispheric coupling associated with different stages of bimanual learning. Evidence is provided that the interaction between hemispheres is of particular importance in the early phase of command integration during acquisition of a novel bimanual task. It is proposed that the dynamic changes in interhemispheric interaction reflect the establishment of efficient bimanual ‘motor routines'. The effects of callosal damage on bimanual coordination and learning are reviewed as well as functional imaging studies related to bimanual movement. There is evidence for an extended cortical network involved in bimanual motor activities which comprises the bilateral primary sensorimotor cortex (SM1), supplementary motor area, cingulate motor area, dorsal premotor cortex and posterior parietal cortex. Current concepts about the functions of these structures in bimanual motor behavior are reviewed.     

A mixed-handed advantage in episodic memory: A possible role of interhemispheric interaction

Recent behavioral and brain imaging data indicate that performance on explicit tests of episodic memory is associated with interaction between the left and right cerebral hemispheres, in contrast with the unihemispheric basis for implicit tests of memory. In the present work, individual differences in strength of personal handedness were used as markers for differences in hemispheric communication, with mixed-handers inferred to have increased interhemispheric interaction relative to strong right-handers. In Experiment 1, memory for words was assessed via recall or word fragment completion. In Experiment 2, memory for real-world events was assessed via recall. Results supported the hypothesis, in that mixed-handers displayed better episodic memory in comparison with strong right-handers.     

Generalizing everyday memory: Signs and handedness

Memory for frequently encountered road signs was investigated. In Experiment 1, the average level of recall of road sign features was found to be only 47%. In Experiment 2, more left-handed than righthanded people recalled that a walking figure faces right on one sign, whereas more right-handed than left-handed people recalled that a digging figure faces left on another sign. Performance thus reflected not a difference in level of mnemonic ability between left-handed and right-handed groups but instead the compatibility between group and task. In Experiment 3, participants were asked to draw any figure walking and any figure digging, with a pattern of results similar to that of Experiment 2. It is suggested that handedness effects in recall are mediated by motor imagery.     

Transsaccadic memory for position and orientation of saccade source and target

Participants made a saccade from one biological-motion figure to another and had to detect saccadecontingent changes in either the walker to which the eyes were sent (the target) or the walker that served as launch site (the source). Intrasaccadic displacements in both source and target were relatively hard to detect, whereas changes in the walkers' depth orientation were readily noticed, indicating that previous findings on within-object saccades generalize to between-objects saccades. Contrary to predictions derived from theories that assign a privileged status to the saccade target, transsaccadic memory for the target's position and orientation was not more accurate than memory for the source. Displacements or rotations of one object toward the other object were more detectable than the same changes away from each other, suggesting that relational coding plays a prominent role in the integration of information across saccades.     

Eye movements and visual memory: detecting changes to saccade targets in scenes

Saccade-contingent change detection provides a powerful tool for investigating scene representation and scene memory. In the present study, critical objects presented within color images of naturalistic scenes were changed during a saccade toward or away from the target. During the saccade,the critical object was changed to another object type, to a visually different token of the same object type, or was deleted from the scene. There were three main results. First, the deletion of a saccade target was special: Detection performance for saccade target deletions was very good, and this level of performance did not decline with the amplitude of the saccade. In contrast, detection of type and token changes at the saccade target, and of all changes including deletions at a location that had just been fixated but was not the saccade target, decreased as the amplitude of the saccade increased. Second, detection performance for type and token changes, both when the changing object was the target of the saccade and when the object had just been fixated but was not the saccade target, was well above chance. Third, mean gaze durations were reliably elevated for those trials in which the change was not overtly detected. The results suggest that the presence of the saccade target plays a special role in trassaccadic integration, and together with other recent findings, suggest more generally that a relatively rich scene representation is retained across saccades and stored in visual memory.     

Depletion of serotonin selectively impairs short-term memory without affecting long-term memory in odor learning in the terrestrial slug Limax valentianus

The terrestrial slug Limax is able to acquire short-term and long-term memories during aversive odor-taste associative learning. We investigated the effect of the selective serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) on memory. Behavioral studies indicated that 5,7-DHT impaired short-term memory but not long-term memory. HPLC (high-performance liquid chromatography) analysis revealed that 5,7-DHT significantly reduced serotonin content in the central nervous system. The present study suggests that acquisition, retention, and/or retrieval of short-term memory involves serotonin, and neither acquisition nor retrieval of long-term memory requires serotonin at a level as high as that required for short-term memory.     

Response-repetition effects in task switching with and without response execution

Previous research into the mechanisms of task switching has shown that repeating the same response in a different task context is associated with costs. To investigate whether such response-repetition costs occur even when the first of the two responses is not overtly executed, we used a variant of the change-signal paradigm. Subjects responded to a first stimulus by pressing a left or right response key. In half of the trials, a second stimulus occurred after a variable, adaptively adjusted delay, indicating to abandon the first response, and only respond to the second stimulus using another set of left and right response keys. In Experiment 1, different tasks had to be performed with the first and second stimulus (task-switch condition); in Experiment 2, the same task had to be performed with both stimuli (task-repetition condition). Response-repetition costs were obtained in Experiment 1, and response-repetition benefits in Experiment 2. Importantly, these costs and benefits were obtained even when the first of the two responses had not been overtly executed. The data support the idea that interference of task-specific response codes occurs at the level of abstract response codes. Interference of such response codes occurs even when the responses are not overtly executed.     

Consistency of handedness, regardless of direction, predicts baseline memory accuracy and potential for memory enhancement

Research has shown that consistently right-handed individuals have poorer memory than do inconsistently right- or left-handed individuals under baseline conditions but more reliably exhibit enhanced memory retrieval after making a series of saccadic eye movements. From this it could be that consistent versus inconsistent handedness, regardless of left/right direction, is an important individual difference factor in memory. Or, more specifically, it could be the presence or absence of consistent right-handedness that matters for memory. To resolve this ambiguity, we compared consistent and inconsistent left- and right-handers on associative recognition tests taken after saccades or a no-saccades control activity. Consistent-handers exhibited poorer memory than did inconsistent-handers following the control activity, and saccades enhanced retrieval for consistent-handers only. Saccades impaired retrieval for inconsistent-handers. None of these effects depended on left/right direction. Hence, this study establishes handedness consistency, regardless of direction, as an important individual difference factor in memory.     

Mode of execution of movement and characteristics of motor short-term memory

Investigations in the area of motor short-term memory (MSTM) have typically used an experimental paradigm in which the experimeter defines the terminal position of a response. This study compares the retention characteristics of movements executed in this manner with those in which the subject is able to define his own terminal position. It was found that whilst the temporal position of an interpolated response affected retention in both modes of execution, the relative magnitude of an interpolated response only interfered with movements executed under the classical MSTM paradigm. Theoretical reasons for this are discussed together with the methodological issues which such a discrepancy raises.     

Working memory capacity and the antisaccade task: individual differences in voluntary saccade control

Performance on antisaccade trials requires the inhibition of a prepotent response (i.e., don't look at the flashing cue) and the generation and execution of a correct saccade in the opposite direction. The authors attempted to further specify the role of working memory (WM) span differences in the antisaccade task. They tested high- and low-span individuals on variants of prosaccade and antisaccade trials in which an eye movement is the sole requirement. In 3 experiments, they demonstrated the importance of WM span differences in both suppression of a reflexive saccade and generation of a volitional eye movement. The results support the contention that individual differences in WM span are not exclusively due to differences in inhibition but also reflect differences in directing the focus of attention.     

Handedness and depression in university students: a sex by handedness interaction

Previous research has indicated that there is an increased incidence of left-handedness in samples of depressed individuals. We administered the Beck Depression Inventory (BDI) to a sample of 541 undergraduate students. Left-handed males showed significant elevation of BDI scores. It is unlikely that this result is due to decreased right hemisphere activity or sex-role conflicts. However, one possibility is that known differences in male steroid hormones levels between right- and left-handers contributed to this effect. Press     

Individual differences in face memory and eye fixation patterns during face learning

This study examined the relationship between individual differences in face memory and eye fixation patterns during face learning. Participants watched short movies of 20 faces and were divided into high and low face memory groups based on their performance in a recognition memory test. No qualitative difference was observed in the eye fixation distribution between high and low groups. Both groups mostly fixed on the internal region of faces, especially the eyes. A difference in the eye fixation pattern by groups was observed in the number of fixations and total fixation time on the eyes, which reflected high face memory participants moving their eyes between the left and right eyes more frequently than low face memory participants. These findings suggest that fixation on the eyes has a functional role in face memory and is related to individual differences in face memory.     

Working memory, strategy execution, and strategy selection in mental arithmetic

A total of 72 participants estimated products of complex multiplications of two-digit operands (e.g., 63 × 78), using two strategies that differed in complexity. The simple strategy involved rounding both operands down to the closest decades (e.g., 60 × 70), whereas the complex strategy required rounding both operands up to the closest decades (e.g., 70 × 80). Participants accomplished this estimation task in two conditions: a no-load condition and a working-memory load condition in which executive components of working memory were taxed. The choice/no-choice method was used to obtain unbiased strategy execution and strategy selection data. Results showed that loading working-memory resources led participants to poorer strategy execution. Additionally, participants selected the simple strategy more often under working-memory load. We discuss the implications of the results to further our understanding of variations in strategy selection and execution, as well as our understanding of the impact of working-memory load on arithmetic performance and other cognitive domains.     

Working memory,strategy execution,and strategy selection in mental arithmetic

A total of 72 participants estimated products of complex multiplications of two-digit operands (e.g., 63 × 78), using two strategies that differed in complexity. The simple strategy involved rounding both operands down to the closest decades (e.g., 60 × 70), whereas the complex strategy required rounding both operands up to the closest decades (e.g., 70 × 80). Participants accomplished this estimation task in two conditions: a no-load condition and a working-memory load condition in which executive components of working memory were taxed. The choice/no-choice method was used to obtain unbiased strategy execution and strategy selection data. Results showed that loading working-memory resources led participants to poorer strategy execution. Additionally, participants selected the simple strategy more often under working-memory load. We discuss the implications of the results to further our understanding of variations in strategy selection and execution, as well as our understanding of the impact of working-memory load on arithmetic performance and other cognitive domains.     

Strategy combination during execution of memory strategies in young and older adults

The present study investigated whether people can combine two memory strategies to encode pairs of words more efficiently than with a single strategy, and age-related differences in such strategy combination. Young and older adults were asked to encode pairs of words (e.g., satellite-tunnel). For each item, participants were told to use either the interactive-imagery strategy (e.g., mentally visualising the two words and making them interact), the sentence-generation strategy (i.e., generate a sentence linking the two words), or with strategy combination (i.e., generating a sentence while mentally visualising it). Participants obtained better recall performance on items encoded with strategy combination than on items encoded with interactive-imagery or sentence-generation strategies. Moreover, we found age-related decline in such strategy combination. These findings have important implications to further our understanding of execution of memory strategies, and suggest that strategy combination occurs in a variety of cognitive domains.     

Interhemispheric interaction and egocentrism: the role of handedness in social comparative judgement

Previous research has shown that people are egocentrically biased when making judgements that require a self-to-peer comparison - leading to above-/below-average effects and comparative optimism/pessimism. Two experiments examined whether interhemispheric brain connectivity (assessed via strength of handedness) is associated with egocentrism in the comparative judgement process. In Experiment 1, strong handers (SH) and mixed handers (MH) made percentile rank judgements about their abilities in easy and hard domains. In Experiment 2, SH and MH judged their likelihoods of outperforming a co-participant in easy and hard tasks. Both experiments showed that SH were more egocentric than MH and thus showed (a) more above- and below-average effects when estimating their abilities (Experiment 1) and (b) generally larger optimism biases when predicting performances in a competition (Experiment 2). Taken together, these experiments provide evidence that underlying interhemispheric connectivity shapes egocentrism in comparative judgement.