Assessment of Attention with the CAB
A complete review of theories of attention would be impossible in this context. However, an overview of issues related to the development of the CAB is important. More comprehensive reviews of the particular theories of attention and attention tasks addressed can be found in Zomeren and Brouwer (1994) and Mirsky, Fantie, and Tatman (1995). Mirsky, Fantie, and Tatman (1995) point out the fact that attention is clearly not a unitary factor and that any attempt to assess attention should address the multifaceted aspects of attention in a systematic way. Assessment of attention should not simply be an incidental function of the other tests used during a neuropsychological evaluation. It should systematically assess various aspects of attention and not be limited to one sensory modality. The following is an attempt to briefly summarize the two models of these “factors” of attention proposed by Mirsky, et. al. (1995) and Zomeren and Brouwer (1994).
Zomeren and Brouwer (1994) break down attention tasks into two major components, consisting of Selectivity and Intensity. Selectivity is assessed by Focused Attention and Divided Attention tasks. Intensity is divided into Alertness and Sustained Attention tasks. Focused Attention tasks require attention to be directed to one aspect of sensory information to the exclusion of others. This can be assessed by requiring the subject to attend to one of several competing sensory inputs (sensory information channels) or one of several dimensions of a single sensory input (attributes). Divided Attention tasks require a subject to divided and/or share their attentional capacity between two or more aspects of sensory information or two or more types of mental operations. It is clear that both of these types require Selectivity of sensory information. The fundamental difference between these two aspects is that focused attention tasks require the subject to respond (attend) to relevant stimuli and not respond (ignore) to other types of dimensions of sensory inputs (distractors). Errors on this type of task can be produced by problems with distraction or response interference. During divided attention tasks, all sensory information being provided should be processed (attend) even though different sensory information is provided and different responses be required to different sensory information. Examples of focused attention tasks in the CAB include the Discriminate Reaction Time Test (distraction) and the Stroop Interference Cancellation Test (distraction and response interference during the auditory interference trials). Divided attention is assessed using the Auditory/Visual Multi-processing Test.
The second major component of attention tasks is Intensity. Intensity tasks are broken into two categories; Alertness and Sustained attention tasks. Alertness is assessed by a person’s ability to maintain arousal levels and features of “contingent negative variations” (i.e., variations in psychophysiological state [expectancy] to stimulus). Alertness can also be defined as phasic alertness. Phasic alertness refers to a neurophysiological process taking place in a person who is expecting a relevant stimulus in the immediate future (Zomeren & Brouwer, 1994). Postner (1975) describes alertness as a hypothetical state of the central nervous system that affects a subject’s general receptivity to stimulation. This involves both the subject’s orientation to a stimulus and their readiness to produce a motor output in response to the stimulus. Therefore, Alertness is made up of the relationship between expectancy (contingent negative variations), orientation to various stimuli, and readiness to produce a motor output. Since a subject’s basic level of alertness is a fundamental component of all cognitive tasks the CAB assesses this feature using both a pure auditory and pure visual Reaction Time test (Go Trials). If performance on the Auditory/Visual Reaction Time Test is impaired the examiner should consider issues related to these particular tests before interpreting any other measure of the CAB or any neuropsychological test for that matter. Impaired pure reaction time could mean that fundamental alertness is impaired (possibly related to factors such as brain stem injury, medication effects, poor sleep, etc.), primary sensory perception/orientation is impaired (subcortical/cortical), motor functioning is impaired, or motivation is questioned. Also, if very significant impairments on these measures are identified and there are no clear reasons for this to be occurring, motivational issues should be considered including faking bad or simulation of impairments. There are several factors why validity concerns are raised if severely impaired performance is identified on this task, without evidence of this impairment through history or observation. This includes the fact that there is little variability on RT in the normal population, significant impairments in alertness should be identifiable through observation, and the extreme difficulty of purposefully adding 100-200ms to RT consistently.
The second variable of the Intensity component is Sustained Attention (Tonic Alertness). Sustained attention is traditionally assessed using Continuos Performance Tests, which are often extended discriminate reaction time measures (Go/No-Goes tasks) lasting 15-20 minutes and broken down into 3 to 5 minute intervals. Sustained attention tasks are designed to assess either a loss of performance over time or variability of performance (instability of concentration). Variables commonly assessed include time-on-tasks, lapses of attention, and intraindividual variability. Time-on-task effects result in reduction in performance as a function of time (opposite of practice effects). Lapses of attention are momentary reductions in performance lasting a few seconds at a time. Intraindividual variability is a more continuous variability in performance. These features are not directly assessed in the CAB but are extensively assessed using various measures of the CAB CPT. Research has shown that many neurobehavioral disorders (e.g., CHI) do not produce impairments in sustained attention once slowed information processing has been controlled for. If there is a need to included sustained attention (Tonic Alertness) there are numerous commercially available CPTs. NeuropsychWorks uses separate tests (The CAB CPT) to specifically address these types of measures. A more in-depth discussion of these variables can be found in the manual for the CAB CPT. There are a number of different types of sustained attention (Tonic Alertness) CPT measures with the CAB CPT. The CAB CPT addresses two different aspects of Tonic Alertness tasks. They are Monitoring and Vigilance measures. The difference between monitoring and vigilance essentially has to do with the frequency the target occurs in relationship to the non-targets or distracters. This is related to the selectivity aspect addressed earlier. On a sustained focused attention task the person needs to attend to certain environmental attributes and ignore (not respond) to others, which are usually within the same sensory modality. On monitoring CPT tasks the selective stimuli attribute occurs frequently. On vigilance CPT tasks the selective stimuli attribute occurs less frequently relative to the total number of stimuli. For the CAB CPT measures this ratio is 1 to 3 versus 1 to 15.
Zomeren and Brouwer (1994) use the term Supervisory Attention Control as the highest level of attention tasks. These tasks require a culmination of most if not all of the abilities already identified. Supervisory Attention Control measures would require multiple strategies for focusing, dividing, switching, and sustaining of attention. These tasks would go beyond a subject’s basic ability in these areas and require a strategy to overcome a subject’s automatic response when faced with a non-routine situation or a disturbance of routine in a well-trained task. The CAB has two tasks that in their most difficult form would assess this ability. The Mixed Auditory/Visual Multiprocessing Test (and the Auditory Distraction part of the Stroop Interference Cancellation Test (SICT). The AVMT becomes a demanding task when the subject is asked to alternate attention between auditory information and visual information (Divided attention task). The subject must shift their mental processing during this divided attention task from attending to alternating sensory information to the cognitive process of determining the midpoint between visual information and auditory information. They must also maintain a working memory of the last sensory input to perform the next expected task. On the Stroop Interference Cancellation Test the subject starts out with a simple cancellation task. Then half way through the task competing auditory information is presented which must be ignored to maintain consistent performance with the initial portions of the task.
Mirsky et. al. (1995) develop a conceptualization of attention that encompasses four primary (separate) factors through a factor analysis of various neuropsychological tasks that have a significant attention requirement. The first element (or factor) of attention is the Focus-Execute ability. Tests assessing this factor traditionally have two elements: a visual-perceptual ability (often rapidly scanning stimulus material for a pre-defined target) and a requirement to make either verbal or skilled manual responses. These would be similar to the Selectivity component (focused and divided attention tasks) described by Zomeren and Brouwer (1994). The CAB uses the auditory and visual tasks of the AVMT and the first 4 parts of the SICT to address this factor.
The second element of attention addressed by Mirsky et. al. is call Shift. The Shift factor is assessed through tasks that require cognitive flexibility for task completion. An assumption is made that these tasks reflect an abstract capacity to shift from attending to one aspect or stimulus feature of the target to another in an adaptive and flexible manner. This ability to shift attention in an adaptive manner appears similar to the Supervisory Attention Control described by Zomeren and Brouwer (1994). The CAB addresses the concept or element of shifting in a more expanded way. It divides shifting into various components. The most basic elements are tasks that simply require the subject to shift attention between different sensory channels (Auditory and Visual) with very little requirement of mental flexibility or abstract reasoning (divided attention measures of the Mixed Scan Reaction Time Test). A more demanding shifting task of the CAB is the Shift Discriminate Reaction Time Test. This is a focused attention task with continually changing targets of different sensory channels, that has considerable interference in that some of the non-targets (No Goes) are similar to the target except that it is in a different sensory modality. An example of this is when the target is the color red and a non-target presented is the word red. The most demanding task in this group is the Mixed Auditory/Visual Multi-processing Test, which is a divided attention task with an in intervening requirement of mental processing and maintenance of a working memory of shifting sensory channels.
The third element proposed by Mirsky et. al. (1995) is the Sustain factor, which includes tasks requiring vigilance over extended periods. This factor, as analyzed by Mirsky et. al., which included a discriminate reaction time test (Go/No-Go), lasting for 7-10 minutes, used total number of hits, commission errors, and reaction time (focused attention). The CAB has both auditory and visual discriminate reaction time tests (Auditory/Visual Discriminate Reaction Time Test) included in the battery, which last 5 minutes each. However, there are many other variables to a sustain factor (Phasic Alertness), as described by Zomeren and Brouwer (1994), which appear to be important. The CAB includes a briefer measures of focused attention (lasting 5 minutes), to address information processing speed and decision making (GO) and inhibiting motor responses (No GO). To address a more comprehensive analysis of the Sustain element of attention a dedicated battery of tools has been developed (CAB CPT). This includes a number of different types of CPT measures, included visual tasks, auditory tasks, mixed sensory mode and self-paced cancellation tasks that extend over a 15 to 20 minute tom frame. See the CAB CPT manual for more specific information regarding these measures.
The forth element proposed by Mirsky et. al. (1995) is the Encode factor. The battery of tests factor analyzed by the authors only included Numerical-Mnemonic type of tasks (Digit Span and Arithmetic from the WAIS-R). They hypothesize that the Encode element assesses the serial incorporation, retention, cognitive manipulation, and ultimate recall of numeric information. The CAB utilizes both an Auditory (numerical-mnemonic task) and a Visual counterpart of this ability. They are the Auditory Encoding Test and the Visual Encoding Test.
In summery, the CAB is designed to assess different aspects or components of attention in a reliable and valid manner. The CAB has measures of Selectivity including tasks requiring focused attention (Discriminate Reaction Time Test and Stroop Interference Cancellation Test) and divided attention (Auditory Visual Reaction Time Test and the Auditory/Visual Multi-processing Test). Measures of Intensity requiring Alertness (Phasic Alertness) and comparable motor output found with other measures of the CAB (To control for motor and alertness variables on later tasks), are the Auditory/Visual Reaction Time Tests. Sustained Attention tasks (Phasic Alertness) are addressed in a limited manner with the Auditory/Visual Discriminate Reaction Time Test. However, a much more in-depth analysis of this element is addressed with the CAB CPT. Finally, the highest order of tasks requiring Supervisory Attention Control would include the Auditory/Visual Multi-processing Test (in its most demanding form) and the auditory distraction portion of the SICT. Focus-execute measures would include the AVMT and the SICT. Shift tests without the Element of Supervisory Attention Control would include the Mixed Scan Reaction Time Test and the Shift Discriminate Reaction Time Test (third task of the Auditory/Visual Discriminate Reaction Time Test). A Shift test with the element of Supervisory Attention Control includes the Mixed AVMT. The Encoding Factor is assessed through the Auditory/Visual Encoding Tests, which includes both Auditory (Numerical-Mnemonic) domain and Visual encoding tasks. Finally, a direct assessment of motivation and effort is addressed utilizing a simple forced choice memory task that is analyzed by comparing the subject’s performance relative to chance probabilities.