What forgetting tells us about remembering: The influence of top–down control on hemispheric asymmetries in verbal memory

Abstract

It has been suggested that left hemisphere (LH) advantages in verbal processing is due to superior top–down control of verbal information. It is not clear how top–down mechanisms affect the encoding and retrieval of verbal information from hemispheric memory and whether they only influence activation or also encompass the inhibition of verbal information. The directed forgetting method, in conjunction with divided visual field presentation, was used to examine the influence of top–down control mechanisms on hemispheric asymmetries in verbal memory. Participants were cued to remember or forget words. Cues were presented either simultaneously with targets or after a short delay. A recognition memory test using divided visual field presentation was then given. Response times (RTs) revealed effects of cue timing in the LH. With simultaneous cues, RTs were faster to “Remember” words compared to “Forget” words. With delayed cues, RTs for “Remember” and “Forget” words were equivalent. In the right hemisphere (RH), “Remember” words were consistently faster than “Forget” words, regardless of cue timing. These data provide evidence that top–down mechanisms influenced LH verbal memory retrieval more than RH verbal memory retrieval. Finally, there was little evidence to suggest the hemispheres differ in inhibitory processing.

Keywords:

• Hemispheric asymmetry
• Top–down control
• Verbal memory
• Executive function

We would like to thank Kira Hawkins, Melanie Howarth, Morgan Oswald, Rachel Thomas, and Ben Tipton for their help in data collection. We would also like to thank the three anonymous reviewers for their helpful comments on the manuscript.

We would like to thank Kira Hawkins, Melanie Howarth, Morgan Oswald, Rachel Thomas, and Ben Tipton for their help in data collection. We would also like to thank the three anonymous reviewers for their helpful comments on the manuscript.

Notes

¹ We note that our usage of “verbal memory” in this introduction refers to both semantic and episodic memory, following previous language of other investigations in this literature. However, data obtained from this study are more consistent with episodic memory rather than semantic memory.

² ANOVAs were also conducted on RTs for miss, correct rejections and false recognitions. There were no significant effects for misses or corrected rejections (both F < 1, p > .1) A main effect of visual field was observed for false recognitions [F(1, 63) = 10.10, p = .002, ]. RTs for false recognitions were faster in the RVF-LH (M = 914) than in the LVF-RH (M = 1012). No significant interaction was observed for false recognition RTs.

³ A 2 (Visual Field) × 2 (Cue Type) repeated-measures ANOVA was conducted on RT medians for data within each Cue Timing condition. In the Simultaneous Cue condition, there was a significant Visual Field × Cue Type interaction [F(1, 31) = 4.22, p = .048, ]. Post hoc pairwise t test replicated results from the RT mean analysis, suggesting that RT medians were lower in the RVF-LH than in the LVF-RH [t(31) = 2.192, p = .036]. No significant interaction was observed in the Delayed Cue condition, also replicating results from the RT mean analysis.

⁴ RT medians were also analysed to rule out the influence of outliers. A 2 (Cue Type) × 2 (Cue Timing) mixed-factor ANOVA was conducted on data within each visual field, using RT medians. These analyses replicated the analyses on the RTs means. No Cue Type × Cue Timing interaction in the LVF-RH. In the RVF-LH, we observed a significant Cue Type × Cue Timing interaction on median RTs [F(1, 63) = 9.90, p = .003, ].