STROOP EFFECTS

Stroop effects and Aging

Stroop Effect-Aging

1. Introduction

The Stroop effect [44] is one of the best-known effects in cognitive psychology. It accounts for cognitive interference, which occurs when the processing of a specific stimulus feature impedes the simultaneous processing of a second stimulus attribute. Naming the ink color of a color word takes much longer than naming the color of a patch of color or reading out a color word. The difference in reaction time (RT) is the so-called Stroop interference effect (for a review see [27]). Virtually everyone who can read shows a robust Stroop effect from early age on. The Stroop task is [44] is probably the classic paradigm to study cognitive control [10] and the Stroop effect seems a good measure for frontal lobe function and inhibitory processes, a construct repeatedly invoked to explain cognitive deficits associated with aging (e.g. [20]). The Stroop task is an ideal tool for studying typical and atypical development of executive processes and has been used in several studies to investigate aging processes [25], [31], [1], [38] and [42]. Clinical and recent neuroimaging studies showed the relevance of the medial and lateral frontal cortex for Stroop interference [50], [31], [29], [13] and [55].

A quantitative comparison of the activation patterns resulting from fMRI studies to test hypotheses regarding age-related changes relies on the assumption that the coupling of neural activity to the neuroimaging signal is not affected by aging. Differences in neuroimaging signal response between young and elderly adults can be mapped directly to differences in neural response, only if such coupling does not change with age [11] and [12]. Huettel et al. [23] showed that the amplitude and form of hemodynamic responses for young and elderly adults are similar. But elderly adults showed greater voxelwise noise leading to a smaller spatial extent of activation. An fMRI study by Nielson et al. [34] showed that although task performance and activation pattern differed, the underlying hemodynamic response was comparable between younger and older adults. In contrast, Taoka et al. [46] found the time lag of the hemodynamic response in fMRI to be prolonged with increasing age. In a blocked design study, the latency of the trailing edge of the hemodynamic response tends to increase with age [38]. In summary, one can assume that with normal, healthy aging, the neuronal coupling remains intact, even if the temporal dynamic might change.

The basic aim of the present fMRI study was to compare the neural processes and the hemodynamic response underlying the color-word Stroop interference task for healthy young and middle-aged adults. For this, a single trial version of the paradigm used in previous fMRI-studies [55], [36] and [32] and functional near-infra-red studies [43] and [41] was applied to test adults of varying age. The use of a single trial design allowed us to characterize the hemodynamic response in accordance with age. Further, changes in reaction time and the interference effect were investigated.

2. Method

2.1. Subjects

Forty-seven healthy subjects (24 women) of different age were ...