Memory encoding in healthy older adults using neutral, perceptual, and semantic tasks

Memory encoding can be perceptual processing based on shapes, colors, or size, or semantic processing based on the objects' implicit meaning in nature (Nicolas, 1998). This study investigates how encoding conditions are associated with healthy older adults' recognition performance, as well as how they process information perceptually and semantically, using the event-related potential (ERP) technique. Thirteen subjects (age 65.2 ± 4.6) participated in the behavioral and ERP experiment. They were instructed to encode 80 Chinese characters on a study-recognition memory paradigm. The characters were shown on a computer screen. Three conditions were set up, namely, neutral (no memorization instruction), perceptual (i.e. to judge word configuration), and semantic (i.e. to judge word's semantic meaning). Behavioral results showed that the semantic condition had the highest recognition rate (74%; range: 46–93%; d′ = 1.16). However, this rate did not differ statistically (p = 0.41) from the recognition rate (73%; range: 63–89%; d′ = 1.08) in the neutral condition. The perceptual encoding condition demonstrated lowest recognition accuracy (60.19%; range: 46–85%; d′ = 0.81) when compared to both the neutral (p < 0.03) and semantic conditions (p < 0.02). Analysis of ERP data using repeated measure ANOVAs showed that the negative component (maximum in the left frontal region) between 240 and 360 ms in both neutral and semantic conditions were significant for memory effect (p < 0.01 and p = 0.03, respectively). Positive-going potentials between 360 and 700 ms (P550) were significant for memory or interaction effects in all three conditions. Non-significance in behavioral data between neutral and semantic encoding conditions appears to indicate that healthy older adults can perform semantic processing. ERP results seem to agree with this interpretation. The negative component between 240 and 360 ms may be associated with semantic processing (Mangels et al., 2001) since both neutral and semantic conditions showed significant memory effect, but not in the perceptual condition. The frontal and parietal positive potentials between 360 and 700 ms may indicate their preserved ability to perform additional processing for successful encoding (Friedman, Nessler, and Johnson, 2007). Inclusion of different age or clinical groups would have allowed further analysis on group differences and would strengthen these conclusions.