Short-term and Working Memory in Blind and Sighted Individuals

This thesis examines the impact of visual deprivation on memory abilities. Although some studies report those who are blind appear to exhibit larger short-term memory (STM) capacity relative to the sighted, the extent to which this generalizes to nonverbal information and more complex memory tasks is unclear. The first chapter presents results of a systematic review evaluating visual deprivation’s impact on STM and on working memory (WM). Age of blindness onset, stimulus type, and demographics are possible factors explaining discrepancies across studies.Subsequent chapters detail the results of two empirical studies exploring the roles of verbal and nonverbal stimuli along with sensory modality in STM and WM among individuals who are sighted and visually impaired. In a test of verbal and nonverbal memory, sighted and congenitally blind adults completed a battery of auditory short-term, working, and recognition memory tasks using difficulty-matched verbal and nonverbal information. These results find that while blind individuals exhibit a verbal memory advantage over sighted individuals, their advantage is eliminated for nonverbal memory. A second set of experiments investigates how encoding information using different modalities may impact STM and WM in legally blind and sighted adults matched for socioeconomic status (SES). Overall, blind participants outperformed sighted ones on both the STM and simpler WM tasks. Critically, blind participants also outperformed sighted participants on a more complex WM task, but this group difference only appeared when SES factors were equated across the groups. Moreover, whereas sighted participants had improved STM for items encoded visually as compared to for items heard orally, blind participants performed equally well between braille encoded and heard information. Thus, STM performance in individuals who are blind appears to extend to robust encoding through multiple sensory modalities. In conclusion, Data from these three studies suggests considering whether stimuli are verbal or nonverbal and encoding modality are important for memory. Overall, the findings presented here are consistent with the hypothesis that in cases when blind individuals exhibit a memory advantage over the sighted, it is linked to experience-dependent plasticity. These findings have potential to aid in designing more effective educational and rehabilitative interventions capitalizing on the increased capacity for verbal memory in blindness