Five tasks were nominated by scientists as promising measures of control of attention for the purposes of CNTRICS: (1) an Attention Capture Task,30
(2) an Attention Networks Task,31,32
(3) a Distractor Condition Sustained Attention Task (dSAT) (E. Demeter, M. Sarter, C. Lustig [personal communication] and McGaughy and Sarter33
), (4) a Guided Search Task,25,34
and (5) a Spatial Cueing Task.35,36
After initial discussion of the 5 nominations, the CNTRICS working group on control of attention concluded that the Attention Networks Task included potentially valuable measures of alerting, orienting, and conflict aspects of attention but did not include a measure of control of attention in response to an internal representation. Thus, the measures of that task were excluded from further consideration as an index of control of attention.
Of the remaining 4 nominated tasks, 2 paradigms for measuring control of attention were judged as the most promising for further development for work on schizophrenia at this time—the Guided Search paradigm and the dSAT. These 2 paradigms and their supporting research will be described in detail in the following sections of this article. It is noteworthy that they were viewed by the CNTRICS working group as equally promising but with strengths in differing areas.
The Guided Search paradigm involves search for a target in a visual array using some feature of a subset of stimuli to limit search to only the stimuli that include that feature.25,37
It was judged to have very strong construct validity as a measure of the ability to guide the focus of attention using an internal representation, has clear links to specific cognitive mechanisms, is easily adaptable for human neuroimaging studies, and is known to detect a noteworthy top-down processing deficit in schizophrenia. Several studies also indicate a link of guided search processes to specific neural regions. On the other hand, the Guided Search task used in humans has not been applied in the same form in animals, although the group believed that it could be successfully adapted for application for monkeys and perhaps in an adapted form for nonprimate animals.
The dSAT involves detection of a signal (eg, a brief focal light illumination) in a series of discrete trials under distractor conditions (eg, changing overall lighting intensity) as compared to nondistractor conditions [E. Demeter, M. Sarter, C. Lustig (personal communication)]. It was judged to have a particular advantage in applicability to several species of animals as well as to humans because it was initially developed as a sustained attention paradigm for rat research. Its links to neural circuits were viewed as well documented, including through studies involving neuropharmacological manipulations, thereby strengthening the task's applicability for new drug development. The dSAT was also viewed as easily amenable to human neuroimaging studies and as having construct validity as a measure of control of attention that was nearly as strong as the Guided Search paradigm. In contrast, the specific cognitive mechanisms that underlie performance on the dSAT were believed to be only partially understood. Furthermore, the task is only beginning to be applied to schizophrenia patients.
The Attention Capture Task was viewed as having strong construct validity as a measure of the control of attention because it examines the response cost of introducing salient but task-irrelevant stimuli within a search for other relevant stimuli. In a Fan et al31
version of this task, eg, subjects are exposed to a rapid-onset set of small circles in a cue array and then search a visual array for a target that is a rapid-onset “×” or “=” character.31
To the extent that attention is captured by the irrelevant stimulus in the initial cue array, RTs are slowed. However, the links of the measures in the Attention Capture paradigm to neural circuits were judged to be only moderately understood, the cognitive mechanisms were only partially explicated, and its ability to detect impairment in schizophrenia was unknown. While the working group believed that an animal version could be developed for this task, it was not aware of any current version.
The Spatial Cueing Task developed by Posner36
involves spatial cues in the periphery of the visual field that precede the detection of targets on the same or opposite side of the visual field. The RT to valid (same side) cues and invalid (opposite side) cues are typically the primary indices of the benefits and costs of spatial orienting of attention. Another aspect of performance is slowing of RTs to valid cues if the delay between cue and target is more than 250 ms, believed to represent a relatively automatic inhibitory mechanism that protects one against redirection of attention to previously scanned locations that were insignificant.38
The CNTRICS working group on control of attention considered this task to be of considerable interest as a spatial orienting of attention measure but thought that it was only moderately related to control of attention by an internal representation. While the cognitive mechanisms and neural circuits underlying this task are well understood, the group noted that the available literature is inconsistent regarding the task's sensitivity to a key attentional impairment in schizophrenia. Its sensitivity to neuropharmacological manipulations was also felt to be only moderate. Thus, the other nominated tasks were judged to be more promising measures of deficits in control of attention in schizophrenia.
The 2 most highly regarded CNTRICS tasks for measuring control of attention are described and reviewed in much more detail in the sections that follow.