Privileged Access by Irrelevant Speech to Short-term Memory: The Role of Changing State

Memory for visually presented items is impaired by speech that is played as an irrelevant background. The paper presents the view that changing state of the auditory material is an important prerequisite for this disruption. Four experiments studied the effects of sounds varying in complexity in an attempt to establish which features of changing state in the auditory signal lead to diminished recall. Simple unvarying or repetitive speech sounds were not sufficient to induce the irrelevant speech effect (Experiment 1): in addition, simple analogues of speech, possessing regular or irregular envelopes and using a range of carriers, failed to imitate the action of speech (Experiment 2). Variability of between-utterance phonology in the irrelevant stream (Experiment 3) emerged as a crucial factor. Moreover, predictability of the syllable sequence did not reduce the degree of disruption (Experiment 4) suggesting that supra-syllabic characteristics of the speech are of little importance. The results broadly support the idea that disruption of short-term memory only occurs when the speech stream changes in state. It is argued that disruption occurs in memory when cues to serial order based on phonological representations of heard material interfere with the phonological codes of visual origin. It is suggested that cues to changing state of the speech input contaminate those associated with items of visual origin, which are already in a phonological store.     

Cerebral White Matter Integrity and Cognitive Aging: Contributions from Diffusion Tensor Imaging

The integrity of cerebral white matter is critical for efficient cognitive functioning, but little is known regarding the role of white matter integrity in age-related differences in cognition. Diffusion tensor imaging (DTI) measures the directional displacement of molecular water and as a result can characterize the properties of white matter that combine to restrict diffusivity in a spatially coherent manner. This review considers DTI studies of aging and their implications for understanding adult age differences in cognitive performance. Decline in white matter integrity contributes to a disconnection among distributed neural systems, with a consistent effect on perceptual speed and executive functioning. The relation between white matter integrity and cognition varies across brain regions, with some evidence suggesting that age-related effects exhibit an anterior–posterior gradient. With continued improvements in spatial resolution and integration with functional brain imaging, DTI holds considerable promise, both for theories of cognitive aging and for translational application.     

Effects of aerobic exercise training, age, and physical fitness on memory-search performance

We investigated the effects of exercise training on memory performance. One group of 13 men (M = 42.92 years of age) participated in supervised aerobic exercise (jogging) three times a week for 12 weeks. A second group of 15 men (M = 43.67 years of age) performed anaerobic exercise (strength training) for the same period of time. Subjects' reaction time (RT) performance in a memory-search task was assessed both before (Time 1) and after (Time 2) the 12 weeks of exercise training. Results indicated that there was no significant change in memory-search performance over time as a function of exercise training. Analyses of the Time 2 RTs demonstrated that aspects of memory-search performance were related significantly both to subjects' initial (Time 1) level of fitness and to age, but not to the amount of change in fitness associated with aerobic exercise training over this 12-week duration in this age group.     

Adult Age Invariance in Sentence Unitization

We examined age differences on a letter detection task that was performed on four-word sentences in order to examine how letter-level and word-level processing is integrated with sentence-level unitization. Sentence-level unitization is defined as the formation of a sentence-level code that delays access to letter-level or word-level codes. There was a consistent word-frequency disadvantage for both age groups in which it took longer to detect letters within high and medium high frequency words than in low frequency words. This finding suggested that word-level and letter-level input channels were involved in a parallel “horse race” to the central processor while simultaneously outputting codes to the sentence-level at the second tier of processing. The present data also revealed that both age groups showed a larger relative increase in reaction time for letter detection for the fourth word position compared to the third word position on syntactically “intact” sentences relative to syntactically “scrambled” sentences. These data indicated that both age groups formed sentence-level codes that made letter-level codes more difficult to access. Finally, older adults' data showed a larger cost than younger adults' data for scrambled sentences than for intact sentences. These results suggest that older adults are more reliant on a syntactical processor that facilitates the parafoveal preview during the reading of syntactically intact sentences. These data suggest that whereas there are age differences in the perceptual processing of letters and words, sentence unitization and syntactical processing remain intact with increasing adult age.     

Human Sensitivity To Concurrent Schedules Of Reinforcement: Effects Of Observing Schedule-correlated Stimuli

The determinants of human sensitivity to concurrent variable-interval variable-interval schedules of reinforcement have been difficult to identify, in part because of procedural differences separating published experiments. This experiment investigated vigilance to stimuli correlated with concurrent schedules. Across phases, 3 college students were provided with either no schedule-correlated stimuli, an observing response that provided brief access to the stimuli, or a contingency that required the subject to identify the stimulus correlated with the source of each obtained reinforcer. Sensitivity, as quantified by the generalized matching equation, was low when no stimuli were available. When the stimuli were response contingent, 1 subject observed them, and her behavior became more sensitive to the distribution of reinforcers across the concurrent schedules. When the procedure required discrimination of the stimulus correlated with each reinforcer, the other 2 subjects also observed the stimuli, and their schedule sensitivity was increased as well. These results implicate procedural differences, rather than inherent behavioral differences, as the source of differences in sensitivity to schedules of reinforcement between humans and nonhumans.     

Age similarities in the inertial properties of attention.

Adult age differences in the mode of allocation of visual attention were investigated, using a visual search task with a circular display containing one target letter and seven distractor letters. In two experiments, a total of 56 younger adults (M = 20 years) and 56 older adults (M = 66 years) searched for a target appearing with equal probability at one of two cued locations. The first cue appeared 115 msec before display onset, and the second cue appeared with display onset; distance between the two cued locations was varied. Target identification performance indicated that attention was inertial, in that reaction time for second-cued targets was related either to the area of the portion of the visual field containing possible target locations or to the mean path length of a serial self-terminating search. There were no age-related decrements in the allocation of visual attention.     

The role of age and perceptual symbols in language comprehension

Older and younger participants read sentences about objects and were then shown a picture of an object that either matched or mismatched the implied shape of the object in the sentence. Participants' response times were recorded when they judged whether the object had been mentioned in the sentence. Responses were faster in the shape-matching condition for all participants, but the mismatch effect was stronger for older than for younger adults, even when the larger variability of the older group's response times was controlled for. These results suggest that older adults may construct stronger situation models than younger adults.