Increased Early Processing of Task-Irrelevant Auditory Stimuli in Older Adults

Abstract

The inhibitory deficit hypothesis of cognitive aging posits that older adults' inability to adequately suppress processing of irrelevant information is a major source of cognitive decline. Prior research has demonstrated that in response to task-irrelevant auditory stimuli there is an age-associated increase in the amplitude of the N1 wave, an ERP marker of early perceptual processing. Here, we tested predictions derived from the inhibitory deficit hypothesis that the age-related increase in N1 would be 1) observed under an auditory-ignore, but not auditory-attend condition, 2) attenuated in individuals with high executive capacity (EC), and 3) augmented by increasing cognitive load of the primary visual task. ERPs were measured in 114 well-matched young, middle-aged, young-old, and old-old adults, designated as having high or average EC based on neuropsychological testing. Under the auditory-ignore (visual-attend) task, participants ignored auditory stimuli and responded to rare target letters under low and high load. Under the auditory-attend task, participants ignored visual stimuli and responded to rare target tones. Results confirmed an age-associated increase in N1 amplitude to auditory stimuli under the auditory-ignore but not auditory-attend task. Contrary to predictions, EC did not modulate the N1 response. The load effect was the opposite of expectation: the N1 to task-irrelevant auditory events was smaller under high load. Finally, older adults did not simply fail to suppress the N1 to auditory stimuli in the task-irrelevant modality; they generated a larger response than to identical stimuli in the task-relevant modality. In summary, several of the study's findings do not fit the inhibitory-deficit hypothesis of cognitive aging, which may need to be refined or supplemented by alternative accounts.

Fig 1. Illustration of an Experimental Run.

Example sequence of auditory and visual stimuli. Participants performed an oddball task in each modality while instructed to ignore the other. Targets in the auditory-attend task were designated by frequency, and targets in the visual task were specific letters.

Fig 2. Illustration of the frontocentral cluster of electrode sites used for ERP measurements of the N1 component.

Fig 3. Depiction of the grand average ERP waveforms for all 4 Age Groups.

ERPs measured in response to auditory standard and novel stimuli at a cluster of electrodes between Fz and Cz. Arrow indicates the auditory N1 wave.

Fig 4. Mean amplitude of the auditory N1.

N1 amplitude averaged across standard and novel auditory stimuli for each task and age group. Error bars represent standard deviation.

Fig 5. Scatterplot of N1 mean amplitude.

Mean amplitude calculated across auditory ignore tasks (low load and high load) and stimulus types. Regression: N1 amplitude (μV) = -3.987–.040 (age).