The authors used a lexical-decision task in 3 different experiments to examine whether age differences in word recognition were consistent across processing stage. In all experiments, word frequency and length were manipulated. In Experiments 1 and 2, encoding difficulty was varied, and in Experiment 3, response selection difficulty was varied. In all 3 experiments, there were no age differences for word frequency. However, in Experiments 1 and 2, older adults showed a larger decrement for encoding. In Experiment 3, age differences were larger when response selection load increased. These results suggest that age differences in word recognition occur because older adults exhibit primarily peripheral-rather than central-processing decrements. The implications of these data for generalized and localized slowing models are discussed.

We examined adult age differences in the impact of redundancy and perceptual noise during visual search. Using a two-choice, visual search task, subjects responded to letters presented in one to four corners of an imaginary display square. On each trial, one, two, or three instances of a given target letter were presented. In the target-plus-noise condition, all nontarget corners of the imaginary square were filled with distractor (i.e., noise) letters. In the target-only condition, all nontarget corners were left blank. The results indicated that older adults showed relatively greater redundancy benefits than the young adults for the target-plus-noise trials than for the target-only trials. These results are interpreted within an internal noise framework.

The authors compare older adults' lexical-decision data with younger adults' data reported in P. Allen, A. F. Smith, et al. (2002). On the basis of their work, it was proposed that consistent-case wordswould be processed by the faster holistic (magnodominated) stream, but that mixed-case words would be processed by the slower analytic (interblob-dominated or blob-dominated) steams. Hue mixing was predicted to have no effect on consistent-case performance, but mixed-hue/mixed-case words were predicted to be recognized faster than monochrome/mixed-case words. Younger adults showed the predicted results, but older adults did not. These results suggest that holistic central processes are maintained, but that older adults exhibited an analytic decrement

In this project we examined the effect of adult age on visual word recognition by using combined reaction time (RT) and accuracy methods based on the Hick-Hyman law. This was necessary because separate Brinley analyses of RT and errors resulted in contradicting results. We report the results of a lexical decision task experiment (with 96 younger adults and 97 older adults). We transformed the error data into entropy and then predicted RT by using entropy values separately for exposure duration (thought to influence peripheral processes) and word frequency (thought to influence central processes). For exposure duration, the entropy-RT functions indicate that older adults show higher intercepts and slopes than do younger adults, suggesting an encoding decrement for older adults. However, for word frequency, older adults show higher intercepts but not steeper slopes than younger adults. Older adults thus show a peripheral processing decrement but not a central processing decrement for lexical decision.

We examined the impact of target redundancy for target-plus-noise (TPN) and target-only (TO) trials. Experiment 1 manipulated response selection load (two-choice vs go/no-go) and Experiment 2 (all two-choice) varied noise redundancy (single or cumulative noise letters) on a visual search, divided attention task in which target letters were presented in one, two, or three corners of a four-corner display. Half of the trials also included noise letters. For Experiment 1, there was a definite redundancy gain for TO trials. Furthermore, older adults, relative to young adults, evidenced an even larger redundancy gain for TO trials than for TPN trials, although response selection load did not interact with age. These results are consistent with the notion that older adults exhibit a processing resources decrement. For Experiment 2, older adults evidenced a relatively larger redundancy gain for TPN trials than for TO trials, and this was especially the case for TPN trials in which all nontarget locations were filled with noise letters. Experiment 2 results are consistent with the notion that older adults also exhibit a selective attention decrement.