Stroop interference and negative priming (NP) suppression in normal aging J. Mayas a, *, L.J. Fuentes b , S. Ballesteros a a Grupo de Investigacio ´n en Envejecimiento y Enfermedades Neurodegenerativas, Departamento de Psicologı´a Ba ´sica II, Universidad Nacional de Educacio ´n a Distancia, Juan del Rosal 10, 28040 Madrid, Spain b Instituto Universitario de Investigacio ´n en Envejecimiento, Departamento de Psicologı´a Ba ´sica y Metodologı´a, Universidad de Murcia, Avda. Teniente Flomesta 5, 30003 Murcia, Spain 1. Introduction The performances of younger and older adults have been compared in many tasks providing information about the kind of processing that is affected by normal aging. Although there is a great debate about the processes involved in many cognitive tasks, the bulk of evidence shows that older adults are impaired in cognitive processes that involve control or top-down mechanisms, but not in those that can be considered more automatic (e.g., Amieva et al., 2002; Conway and Fthenaki, 2003; Andre ´s et al., 2008; Collette et al., 2009). One task widely used to study age-related changes in controlled processing is the Stroop (1935) task. In this task, participants are presented with colored words that refer to colors, and are asked to respond to the stimulus color. The meaning of the word is the task- irrelevant dimension of the stimulus, and the color in which the stimulus is presented is the task-relevant dimension. In the congruent condition, both dimensions coincide (e.g., the word RED is printed in red), whereas in the incongruent condition they do not (e.g., the word RED is printed in blue). Participants usually respond more slowly in the incongruent than in the congruent condition, and also in a control condition in which the stimuli are not words (e.g., a string of colored Xs, or a set of non-color words). The Stroop interference effect reflects the extra time needed to resolve the conflict generated by the irrelevant but pre-potent dimension of the stimulus, i.e. the word meaning, in the incongruent condition. This conflict is produced by activation of the irrelevant but pre- potent word-reading response which is greater than that of the relevant but weaker color-naming response (e.g., McLeod, 1991; Spieler et al., 1996). Although there are different interpretations about how the conflict is resolved (McLeod, 1991; Aron, 2007, for reviews), one widely accepted view is that suppression processes relying on frontal lobe executive control mechanisms are engaged in preventing the irrelevant dimension from taking control of the response (Kane et al., 2007). Reviewing the literature on age-related changes in the Stroop task, we found that older adults do not always show impaired performance, as measured by a greater Stroop interference effect, compared to younger adults. Age-related differences seem to depend on the task format used and/or whether overall speed has been controlled for or not. For instance, when the traditional card version of the Stroop test is used (Stroop, 1935), older adults clearly show greater interference effects than younger adults (Dulaney and Rogers, 1994; Spieler et al., 1996; Davidson et al., 2003; Belleville et al., 2006; Andre ´ s et al., 2008; Ludwig et al., 2009). However, when an item-by-item version is used, in which stimuli are randomly presented on the computer screen, findings vary. Some authors have found greater Stroop effects in older than younger participants (e.g., Hartley, 1993; West and Bell, 1997; West and Alain, 2000; Davidson et al., 2003; Rush et al., 2006), whereas others have found either small or non-significant age- related differences (Basak and Verhaeghen, 2003; Langley et al., 2005; Borella et al., 2009; Ludwig et al., 2009). These divergent results might depend on whether the authors controlled for overall speed. When transformed scores are used to control for speed, similar Stroop effects have been reported in younger and older Archives of Gerontology and Geriatrics 54 (2012) 333–338 ARTICLE INFO Article history: Received 30 July 2010 Received in revised form 12 December 2010 Accepted 13 December 2010 Keywords: Inhibition NP suppression Stroop interference Aging ABSTRACT Age-related differences in the reduction of Stroop interference were explored by comparing the performance of 18 younger (of mean age: 30.0 Æ 3.9 years) and 18 older healthy adults (of mean age: 75 Æ 7.2 years) in a color-word Stroop task. The aim of this study was to determine whether a decrease in the efficiency of inhibitory mechanisms associated with aging could account for age-related differences in the ability to suppress a pre-potent response. Participants performed a Stroop task to assess Stroop interference and NP suppression concurrently. Results showed a greater Stroop interference in older than in young adults. On the other hand, the NP effect was only reliable in the younger group, the older group not showing NP suppression. These findings suggest that the slowing hypothesis alone cannot explain this pattern of results and that the age-related differences must also involve an inhibitory breakdown during aging. ß 2010 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +34 913 989 685; fax: +34 913 987 958. E-mail address: jmayas@psi.uned.es (J. Mayas). Contents lists available at ScienceDirect Archives of Gerontology and Geriatrics journal homepage: www.elsevier.com/locate/archger 0167-4943/$ – see front matter ß 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.archger.2010.12.012