Age Differences in Entropy: Primary Versus Secondary Memory

Abstract

We report a spatial-memory scanning experiment that was used to measure age differences in entropy. A target grid consisting of four adjacent letters followed by the presentation of a single probe letter was presented on each trial. Half of the trials presented the probe stimulus in the same spatial position was the target letter (i.e., the probe letter was always a member of the positive set), and half of the trials transposed the target letter one, two, or three spaces of the right or left of the original target display position (i.e., different trials). The experiment involved blocks of primary-memory and secondary-memory tasks. Reaction-time and error-rate data, as well as entropy analyses and the fitting of an entropy model (based on Allen, Kaufman, Smith, and Propper, in press) to the empirical data indicated that older adults showed higher entropy levels than young adults. These results are interpreted in a "computational temperature" framework in which older adults' higher computational temperatures result in less efficient spatial, episodic memory functioning.

Cognitive Reserve in Young and Old Healthy Subjects: Differences and Similarities in a Testing-the-Limits Paradigm with DSST

“…cardiovascular and metabolic factors [42], [43]. Apart from these facts, empirical evidence from other studies supports our observations of smaller variability in cognitive performance of older adults, which has been interpreted in the context of age-associated entropy or entropy states of the brain [44], [45].…”

Normal aging increases discriminal dispersion in visuospatial short-term memory.

“…In addition, age-comparative functional neuroimaging studies in humans have supported the prediction that neural distinctiveness decreases from early to late adulthood Carp et al, 2011;Goh et al, 2010;Park et al, 2004;Payer et al, 2006;Voss et al, 2008). At the same time, demonstrations of altered discriminal dispersion in humans have been sparse (but see Allen et al, 1998aAllen et al, , 1998bSara & Faubert, 2000). Informed by findings of increasing discriminal dispersion with greater STM load in younger adults (Anderson et al, 2011;Bays et al, 2009;Bays & Husain, 2008;Bays, Wu, & Husain, 2011;Fougnie et al, 2010;Zhang & Luck, 2008), we hypothesized that increasing set size would exacerbate age-related differences in discriminal dispersion, which we conceptualized as a behavioral indicator of the dispersion of probabilistic perceptual and memory representations.…”

“…Our study was guided by the neural noise hypothesis of aging (Welford, 1981(Welford, , 1984 as well as related predictions of greater discriminal dispersion (Allen et al, 1998a(Allen et al, , 1998b, and reduced distinctiveness of neural representations (Li et al, 2000;Li & Sikström, 2002) with advancing adult age. Evidence from animal models (Hua et al, 2006;Liang et al, 2010;Yang et al, 2009) has suggested higher levels of neural noise in the aging nervous system.…”

“…Conversely, studies using longer retention intervals, complex stimuli, or a combination thereof may lead to different results. For example, Allen et al (1998a) detected a reliable interaction between retention time and age for discriminal dispersion using the Sternberg task to probe primary (100-ms masked retention) and secondary memory (10-s retention with distracter task). This task, more than delayed discrimination, may have posed greater demands on associative binding, which is particularly susceptible to the adverse effects of aging (e.g., Chalfonte & Mitchell, 1996;Li, Naveh-Benjamin, & Lindenberger, 2005;Naveh-Benjamin, 2000;Old & Naveh-Benjamin, 2008;Shing et al, 2010).…”

“…Welford, 1981). These authors reported age differences in memory sensitivity in a memory-scanning task (Allen, 1990;Allen, 1991;Allen et al, 1998a) and in a delayed spatial discrimination task (Allen et al, 1998b), and they successfully fit their model to these data (Allen et al, 1998a(Allen et al, , 1998b. However, other age-comparative studies using delayed discrimination thresholds (indicative of discriminal dispersion) for size, spatial frequency, or motion (Fahle & Daum, 1997;Sara & Faubert, 2000;Faubert & Bellefeuille, 2002;Bennett, Sekuler, & Sekuler, 2007) as well as delayed oculomotor (Sweeney, Rosano, Berman, & Luna, 2001) or manual (Lemay, Bertram, & Stelmach, 2004) responses have failed to find significant age-related differences in the precision of visual short-term memory (STM).…”