Does numerical similarity alter age-related distractibility in working memory?

Abstract

Similarity between targets and distracters is a key factor in generating distractibility, and exerts a large detrimental effect on aging. The present EEG study tested the role of a new stimulus dimension in generating distractibility in visual Working Memory (vWM), namely numerical similarity. In a change detection paradigm a varying number of relevant and irrelevant stimuli were presented simultaneously in opposite hemifields. Behavioral results indicated that young participants outperformed older individuals; however, in both groups numerical similarity per se did not modulate performance. At the electrophysiological level, in young participants the Contralateral Delay Activity (CDA, a proxy for item maintenance in vWM) was modulated by the numerosity of the relevant items regardless of numerical similarity. In older participants, the CDA was modulated by target numerosity only in the same numerical condition, where the total number of (relevant and irrelevant) items increased with increasing target numerosities. No effect was present in the dissimilar numerical condition, where the total number of items did not vary substantially across target numerosity. This pattern was suggestive of an age-related effect of the total number of (relevant and irrelevant) items on vWM. The additional analyses on alpha-band lateralization measures support this interpretation by revealing that older adults lacked selective deployment of attentional and vWM resources towards the relevant hemifield. Overall, the results indicate that, while numerical similarity does not modulate distractibility, there is an age-related redistribution of vWM resources across the two visual fields, ultimately leading to a general decrease in task performance of older adults.

Learning by task repetition enhances object individuation and memorization in the elderly

“…In line with a previous study 56 , we found that numerical similarity (see Stimuli and Procedure section) between colored targets and colored distractors did not influence the performance (see Supplementary Information for further details). We therefore collapsed trials across number of distractors for further analysis.…”

“…The most consistent result in these studies is an age-related reduction both in the amplitude and in the modulation of the CDA as a function of memory load [13][14][15]55,56 , which is thought to reflect the lower vWM capacity of older compared to young adults. Moreover, in DMTS tasks where targets were presented among distractors [13][14][15] (see also 56 for targets and distractors in opposite hemifields), an impaired or delayed distractor suppression mechanism was associated in the elderly with changes in the CDA 13,14 , indicating that older participants were retaining also irrelevant items. Changes were also found in the N2pc 15 , and were linked to an age-related deficit at an earlier cognitive stage, namely during target selection.…”

“…Stimuli and procedure. Participants performed a lateralized delayed match-to-sample task 39 , identical to the one of a previous study 56 69,19]). Each stimulus array consisted of one, two or four colored dots independently presented in each hemifield together with light grey dots, resulting in the same or different number of colored dots across the two hemifields (all experimental conditions were counterbalanced across the two hemifields).…”

“…four 59,76 ). Following previous studies 14,38,39,47,56 , hit rates were defined as 'different' responses in change conditions, while false alarms were 'different' responses in no-change trials. It follows that, in the present study, a conservative response criterion is defined as the tendency to answer 'Same' on change trials and is represented by positive values; vice-versa, a more liberal behavior was considered the tendency to answer 'Different' on no-change trials and is represented by negative values.…”

“…Third, significant main or interaction effects resulting from the main ANOVA were then separately investigated in each session, latency and age group (via paired-samples t-tests, and comparing one vs two and two vs four target-trials for Load-related effects), again employing the 20-ms consecutive time window approach (and two consecutive significant time windows to consider a difference as reliable 56 ).…”