Considering phasic alerting in Alzheimer's disease: comment on Tales et al. (2006).
A. Tales, R. J. Snowden, M. Brown, and G. Wilcock (2006) have questioned the authors' view of a possible interdependence between attentional systems mediating exogenous spatial orienting and phasic alerting as well as the authors' suggestion that phasic alerting deficits in patients with Alzheimer's disease (AD) may be influencing their performance on tests of spatial orienting. Consistent with this possibility, both laboratories have previously demonstrated increased spatial orienting and decreased phasic alerting in patients with AD. In Tales et al.'s current study, however, they have instead suggested that their results provide evidence for functional independence between these attentional systems in AD. In this commentary, the authors address the misinterpretations of their study and evaluate the degree to which Tales et al.'s study addresses the issues that they raise. Given Tales et al.'s difficulty performing analyses on response time data because of variance issues, the presence of a reduced (although not significant) alerting effect in Tales et al.'s AD group (consistent with the authors' previous findings), and a potential floor effect in their measure of alerting, the authors question the validity of Tales et al.'s conclusions and reaffirm their position that not considering interactions among attentional systems can lead to inaccurate characterizations of the mechanisms by which they operate.