Age-Related Slowing: Perceptuomotor, Decision, or Attention Decline?

Abstract

Age-related slowing is well documented but its origin remains unclear. A first validation study (Study 1) performed in 46 participants examined the effect of attention allocation (manipulated through a dual task) on various portions of individual simple reaction time (SRT) distribution (minimum, centile 5, centile 50, and centile 95 RTs). It showed that attention 'deprivation' due to a secondary task is not uniform throughout the distribution but impaired mainly the ability to produce a large number of fast responses. Study 2 investigated in 88 healthy participants age-related slowing of perceptual, motor, decision, and attentional processes using SRT and choice reaction time (CRT), finger tapping, and visual inspection time tests. It showed that the majority of SRT slowing after the age of 40 is due to lengthening of centile 5 RT, suggesting perceptuomotor slowing, an interpretation supported by longer visual inspection time and lower tapping frequency. After 60 years, SRT lengthening was due to a further lengthening of the centile 5-centile 50 SRT index, suggesting the participation of attentional decline. These findings support the hypothesis that age-related slowing in simple repetitive tasks is mainly related to slowing at the stage of perceptuomotor processes, and after 60 years, to additional decline of attention.

Psychomotor Slowing in Mild Cognitive Impairment, Alzheimer’s Disease and Lewy Body Dementia: Mechanisms and Diagnostic Value

“…The contribution of associated small infarct revealed by MRI in 13 patients was ruled out as an additional analysis performed in patients without vascular lesions yielded exactly the same results. In AD, the slowing was uniform across the SRT distribution (since both the 5th and 50th percentile SRTs were lengthened) and was thus suggestive of impaired perceptual and motor processes [8] . This interpretation is fully supported by the observed slowdown in finger tapping and a longer VIT.…”

“…These analyses indicate that SRT was longer in both AD and LBD but that the respective patterns differed. In AD, the SRT lengthening concerned both the 5th and 50th percentiles and hence was uniform across the distribution -a pattern that is suggestive of slower perceptuomotor processes [8] . In contrast, LBD patients were able to perform a few rapid responses (as shown by the lack of change in the 5th percentile) but were unable to sustain this ability throughout the test (as shown by longer 50th percentile SRTs) ( fig.…”

“…600 pixels; refreshment rate: 60 Hz) using a method described previously [8] . Briefly, white stimuli were displayed on the center of a black screen.…”

“…In the SRT test, the subject had to respond to any of the letters by pressing the same response button with the index finger, whereas in the CRT test, the 4 letters were classified into two groups (group 1: letters 'H' and 'T'; group 2: letters 'C' and 'S') and subjects were instructed to choose which letter group had been displayed by pressing one of the two response buttons with the index or middle finger. In the SRT test, dependent variables were the numbers of anticipations and omissions and the 5th and 50th percentiles of the SRT [8] ; for the CRT test, the error rate, the median CRT, the standard deviation and the decision time (estimated by subtracting the SRT from the CRT [35] ) were used.…”

“…Reaction time (RT) slowing is usually attributed to attention deficit, but its mechanism has not been specifically addressed. Validation of RT slowing as a diagnostic marker first requires determination of its mechanism; this is now possible with a validated battery assessing the speed of the four components of RT (perceptual, motor, decision and attention processes) [8] .…”