The Effects of Repeated Testing, Simulated Malingering, and Traumatic Brain Injury on Visual Choice Reaction Time

Abstract

Choice reaction time (CRT), the time required to discriminate and respond appropriately to different stimuli, is a basic measure of attention and processing speed. Here, we describe the reliability and clinical sensitivity of a new CRT test that presents lateralized visual stimuli and adaptively adjusts stimulus onset asynchronies using a staircase procedure. Experiment 1 investigated the test-retest reliability in three test sessions performed at weekly intervals. Performance in the first test session was accurately predicted from age and computer-use regression functions obtained in a previously studied normative cohort. Central processing time (CentPT), the difference between the CRTs and simple reaction time latencies measured in a separate experiment, accounted for 55% of CRT latency and more than 85% of CRT latency variance. Performance improved significantly across the three test sessions. High intraclass correlation coefficients were seen for CRTs (0.90), CentPTs (0.87), and an omnibus performance measure (0.81) that combined CRT and minimal SOA z-scores. Experiment 2 investigated performance in the same participants when instructed to feign symptoms of traumatic brain injury (TBI): 87% produced abnormal omnibus z-scores. Simulated malingerers showed greater elevations in simple reaction times than CRTs, and hence reduced CentPTs. Latency-consistency z-scores, based on the difference between the CRTs obtained and those predicted based on CentPT latencies, discriminated malingering participants from controls with high sensitivity and specificity. Experiment 3 investigated CRT test performance in military veterans who had suffered combat-related TBI and symptoms of post-traumatic stress disorder, and revealed small but significant deficits in performance in the TBI population. The results indicate that the new CRT test shows high test-retest reliability, can assist in detecting participants performing with suboptimal effort, and is sensitive to the effects of TBI on the speed and accuracy of visual processing.

Keywords: aging; concussion; effort; feigning; head injury; reliability; response selection; timing precision.

Figures

FIGURE 1

The visual feature conjunction task. Subjects performed a visual feature conjunction task with colored letters (blue P, blue F, orange P, or orange F) subtending 0.5° of visual angle randomly presented to the left or right hemifield, 1.6° from the fixation cross. Stimulus durations were 200 ms. Right-handed subjects pressed the left mouse button for targets (blue P’s, probability 40%) and pressed the right mouse button for non-targets, i.e., letters which resembled the target in color, shape, or neither feature (probability 20% each). The response button could be spatially compatible (trials 1 and 2) or spatially incompatible (trial 3) with the stimulus visual field. Stimulus onset asynchronies (SOAs) began at 2500 ms and were either reduced by 3% following each pair of successive hits or increased by 3% following each miss. From Woods et al. (2015c).

FIGURE 2

Mean choice reaction times (CRTs) as a function of age. CRTs were averaged over stimulus types for subjects of different ages from normative data (Norm), Experiment 1A, Experiment 2 (malinger), and Experiment 3 (TBI). The age-regression slope for the normative data is shown. CRTs for patients with mild TBI (mTBI, filled red circles) and severe TBI (sTBI, circles with vertical red stripes) are shown separately.

FIGURE 3

Minimal stimulus onset asynchronies (mSOA) for subjects as a function of age. Showing data from the normative study (Norm), Experiment 1A, Experiment 2 (Malinger), and Experiment 3 (TBI). mSOAs for patients with mild TBI (mTBI, filled red circles) and severe TBI (sTBI, circles with vertical red stripes) are shown separately.

FIGURE 4

Mean central processing times (CentPT) as a function of age. CentPTs were averaged over stimulus types from control subjects in the normative study (Norm) and Experiment 1A, simulated malingerers (Experiment 2), and TBI patients (Experiment 3). The age-regression slope for the normative data is shown. The results from patients with mild TBI (mTBI, filled red circles) and severe TBI (sTBI, circles with vertical red stripes) are shown separately.

FIGURE 5

Choice reaction time and Omnibus z-scores. Data from control subjects in the normative data (Norm) and Experiment 1A, simulated malingerers (Experiment 2), and TBI patients (Experiment 3). Z-scores were calculated based on age- and computer-use regression slopes from the normative data. Patients with mild TBI (mTBI, filled red circles) and severe TBI (sTBI, circles with vertical red stripes) are shown separately. The data from four simulated malingerers with z-scores outside the range of the figure are not shown.

FIGURE 6

Test–retest reliability of CRTs. CRTs in Experiment 1a plotted against CRTs in Experiments 1B,C. Pearson correlations across repeated tests were 0.72 (Experiment 1A vs. Experiment 1B), 0.74 (Experiment 1A vs. Experiment 1C) and 0.77 (Experiment 1B vs. Experiment 1C).

FIGURE 7

Z-scores for CentPT (central processing time) and CRT. Data from controls in the normative study (Norm) and Experiment 1A, simulated malingerers, and patients with mild TBI (mTBI, filled red circles) and severe TBI (sTBI, circles with vertical red stripes). Z-scores were calculated using the age- and computer-use regression slopes from the normative data. The solid vertical red lines show limits for abnormally (p < 0.05) short and long CPTs.

FIGURE 8

Latency-consistency and Omnibus z-scores. Data are shown from control subjects in the normative population (Norm) and Experiment 1A, simulated malingerers, and patients with mild TBI (mTBI, filled red circles) and severe TBI (sTBI, circles with vertical red stripes). The red lines show abnormality cutoffs (p < 0.05) based on the normative population. The data from 13 malingering subjects with latency-consistency z-scores > 12.0 are not shown.