In a multiple object tracking (MOT) task, young and older adults attentively tracked a subset of ten identical, randomly moving disks for several seconds, and then tried to identify those disks that had comprised the subset. Young adults who habitually played video games performed significantly better than those who did not. Compared to young subjects (mean age = 20.6 years) with whom they were matched for video game experience, older subjects (mean age = 75.3 years ) showed much reduced ability to track multiple moving objects, particularly with faster movement or longer tracking times. Control measurements with stationary disks show that the age-related decline in MOT was not caused by a general change in memory per se. To generate an item-wise performance measure, we examined older subjects' proportion correct according to the serial order in which individual disks were identified. Correct identifications of target disks declined with the serial order in which targets were selected, suggesting that attentional tracking produced graded outcomes.Word count: 3470

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Increased difficulty with memory for recent events is a well-documented consequence of normal aging, but not all aspects of memory are equally affected. To compare the impact of aging on short-term recognition and temporal order memory, young and older adults were asked to identify the serial position that a probe item had occupied in a study set, or to judge that the probe was novel (had not been in the study set). Stimuli were compound sinusoidal gratings, which resist verbal description and rehearsal. With retention intervals of 1 or 4 seconds, young and older adults produced highly similar overall performance, serial position curves, and proportions of trials on which a correct recognition response was accompanied by an incorrect temporal order judgment. Temporal order errors, which occurred on about one quarter of trials, were traced to two factors: perceptual similarity between the wrongly identified study item and the correct item, and temporal similarity between the wrongly identified item and the correct one. Our results show that short-term visual temporal order memory is well-preserved in normal aging, and when temporal order errors do occur, they arise from similar causes for young and older people.

282Working within a framework of exemplar-similarity models of memory (see, e.g., Estes, 1994;Kahana & Sekuler, 2002;Kahana, Zhou, Geller, & Sekuler, 2007;Medin & Schaffer, 1978;Nosofsky, 1986;Nosofsky & Kantner, 2006), we used sinusoidal luminance gratings as stimuli in a modified Sternberg (1966) recognition task. The metric properties of the grating stimuli were exploited to test a novel prediction generated by combining the exemplar-similarity approach with an explicit, signal detection account of decision making (Wickens, 2002).In exemplar-similarity models of recognition memory, it is assumed that a summed-similarity computation is a basic component of subjects' recognition judgment. This computation sums-over all study items-the p's similarity to each of the study items. According to the model, when this sum reaches or exceeds some critical value, the subject will say "yes," judging that the p had been among the n study items that had just been seen. Following convention, we will use the term target (T ) to designate trials on which p replicated a study item and the term lure (L) to designate trials on which p did not replicate any of the study items. On average, the value of summed similarity on T trials will exceed that on L trials, which means that P(yes) responses on T trials will be higher than those on L trials. The nature of the elements entering into the computation will also tend to produce a systematic difference in the variances of summed-similarity values on T and on L trials, which leads to an unexpected prediction for the slope of z-transformed receiver operating characteristics(zROCs).On T trials, values of summed similarity arise from two quantitatively different sources that differ in their respective variability. The first, far larger source of variability reflects the contribution of the n 1 study items that are not replicated by p. Random selection of study items from a stimulus pool means that some of n 1 study items will be similar to p, and that others will be very different from p. As a result of this random divergence, these n 1 nonmatching study items will contribute a highly variable amount of similarity to the summed-similarity signal for any trial. The second, smaller source of variability in summed similarity on T trials reflects the contribution of the one study item that the p does replicate. Over trials, this study item's representation will tend to be perceptually similar to p-even with the memorial noise postulated by the model. Because that study item and p are physically identical, they are likely to be perceptually similar, despite the random noise associated with the study item's memorial representation. As a result, similarity between this study item and p will vary over a narrow range clustered near 1.0 (Zhou, Kahana, & Sekuler, 2004). In three experiments, we examined connections between item-recognition memory and memory for itemposition information. With sequences of compound gratings as study and probe items, subjects made either itemposition judgments (Experim...

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