Irene T. Armstrong

Age-related performance of human subjects on saccadic eye movement tasks

Abstract We measured saccadic eye movements in 168 normal human subjects, ranging in age from 5 to 79 years, to determine age-related changes in saccadic task performance. Subjects were instructed to look either toward (pro-saccade task) or away from (anti-saccade task) an eccentric target under different conditions of fixation. We quantified the percentage of direction errors, the time to onset of the eye movement (saccadic reaction time: SRT), and the metrics and dynamics of the movement itself (amplitude, peak velocity, duration) for subjects in different age groups. Young children (5–8 years of age) had slow SRTs, great intra-subject variance in SRT, and the most direction errors in the anti-saccade task. Young adults (20–30 years of age) typically had the fastest SRTs and lowest intra-subject variance in SRT. Elderly subjects (60–79 years of age) had slower SRTs and longer duration saccades than other subject groups. These results demonstrate very strong age-related effects in subject performance, which may reflect different stages of normal development and degeneration in the nervous system. We attribute the dramatic improvement in performance in the anti-saccade task that occurs between the ages of 5–15 years to delayed maturation of the frontal lobes.

Deficits in saccadic eye-movement control in Parkinson's disease

In contrast to their slowed limb movements, individuals with Parkinsons disease (PD) produce rapid automatic eye movements to sensory stimuli and show an impaired ability to generate voluntary eye movements in cognitive tasks. Eighteen PD patients and 18 matched control volunteers were instructed to look either toward (pro-saccade) or away from (anti-saccade) a peripheral stimulus as soon as it appeared (immediate, gap and overlap conditions) or after a variable delay; or, they made sequential saccades to remembered targets after a variable delay. We found that PD patients made more express saccades (correct saccades in the latency range of 90-140 ms) in the immediate pro-saccade task, more direction errors (automatic pro-saccades) in the immediate anti-saccade task, and were less able to inhibit saccades during the delay period in all delay tasks. PD patients also made more directional and end-point errors in the memory-guided sequential task. Their inability to plan eye movements to remembered target locations suggests that PD patients have a deficit in spatial working memory which, along with their deficit in automatic saccade suppression, is consistent with a disorder of the prefrontal-basal ganglia circuit. Impairment of this pathway may release the automatic saccade system from top-down inhibition and produce deficits in volitional saccade control. Parallel findings across various motor, cognitive and oculomotor tasks suggest a common mechanism underlying a general deficit in automatic response suppression.

The influence of stimulus direction and eccentricity on pro- and anti-saccades in humans

We examined the sensory and motor influences of stimulus eccentricity and direction on saccadic reaction times (SRTs), direction-of-movement errors, and saccade amplitude for stimulus-driven (prosaccade) and volitional (antisaccade) oculomotor responses in humans. Stimuli were presented at five eccentricities, ranging from 0.5° to 8°, and in eight radial directions around a central fixation point. At 0.5° eccentricity, participants showed delayed SRT and increased direction-of-movement errors consistent with misidentification of the target and fixation points. For the remaining eccentricities, horizontal saccades had shorter mean SRT than vertical saccades. Stimuli in the upper visual field trigger overt shifts in gaze more easily and faster than in the lower visual field: prosaccades to the upper hemifield had shorter SRT than to the lower hemifield, and more anti-saccade direction-of-movement errors were made into the upper hemifield. With the exception of the 0.5° stimuli, SRT was independent of eccentricity. Saccade amplitude was dependent on target eccentricity for prosaccades, but not for antisaccades within the range we tested. Performance matched behavioral measures described previously for monkeys performing the same tasks, confirming that the monkey is a good model for the human oculomotor function. We conclude that an upper hemifield bias lead to a decrease in SRT and an increase in direction errors.

Relation between reaction time and reach errors during visuomotor adaptation

Adaptation of reaching movements to visuomotor transformations is generally thought to involve implicit or procedural learning. However, there is evidence that explicit or cognitive processes can also play a role (Redding and Wallace, 2006 [31]). For example, the early phase of adaptation to a visuomotor rotation appears to involve spatial working memory processes linked to mental rotation (Anguera et al., 2010 [11]). Since it is known that cognitive processes like mental rotation lead to larger reaction times (Georgopoulos and Massey, 1987 [12]), here we explored the relation between reaction time (RT) and reach error reduction. Two groups of subjects adapted their reaching movements to a 60° visuomotor rotation either without RT constraints or with RT limited to 350 ms. In the unconstrained group, we found that adaption rate varied widely across subjects and was strongly correlated with RT. Subjects who decreased hand direction error (DE) rapidly exhibited prolonged RTs whereas little RT cost was seen in subjects who decreased DE gradually. RTs were also correlated with after-effects seen when the visuomotor rotation was removed. Subjects with the longest RTs exhibited the smallest after-effects. In the RT constrained group, all subjects exhibited gradual DE adaptation and large after-effects, similar to the fast responders in the free group. These results suggest that adaptation to a visuomotor rotation can involve processes that produce faster error reductions without increasing after-effects, but at an expense of larger reaction times. Possible candidates are processes related to spatial working memory, and more specifically, to mental rotation.

Repetition deficit in rapid-serial-visual-presentation displays: encoding failure or retrieval failure?

The repetition deficit associated with rapid serial visual presentation (RSVP) has been explained as a repetition-induced blindness, that is, as a perceptual or encoding failure. The repetition deficit was replicated in a standard free-recall RSVP task, and it was shown that participants were able to report the lost item when they were prompted with a retrieval probe. The authors argue that both copies of the repeated items were available in memory but that they were not accessible for report. Hence, they conclude that the repetition deficit in the RSVP task reflects a retrieval failure, not a perceptual failure.

Using eye movements to probe development and dysfunction

Publisher Summary Recording of saccadic eye movements has proved to be a valuable tool for investigation of brain function and dysfunction. Recent neurophysiological studies have revealed that the time from target appearance to saccade initiation can be modeled as an accumulator function in which both baseline and rate of rise of saccade-related activity contribute toward achieving threshold for movement initiation. The chapter reviews recent saccadic eye-movement studies designed to track abilities across development and in disorders of frontal cortex and basal ganglia. Studies can be designed to probe the ability to initiate automatic vs voluntary saccades or to suppress saccades. The accumulator model can be used to explain normal developmental changes in voluntary saccade control that are present in normal development as well as in attention deficit hyperactivity disorder (ADHD), Parkinsons disease (PD), and Tourette syndrome (TS).

Comparing Canadian and American Normative Scores on the Wechsler Adult Intelligence Scale-Fourth Edition

Psychologists practicing in Canada must decide which set of normative data to use for the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV). The purpose of this study was to compare the interpretive effects of applying American versus Canadian normative systems in a sample of 432 Canadian postsecondary-level students who were administered the WAIS-IV as part of an evaluation for a learning disability, attention-deficit hyperactivity disorder, or other mental health problems. Employing the Canadian normative system yielded IQ, Index, and subtest scores that were systematically lower than those obtained using the American norms. Furthermore, the percentage agreement in normative classifications, defined as American and Canadian index scores within five points or within the same classification range, was between 49% and 76%. Substantial differences are present between the American and Canadian WAIS-IV norms. Clinicians should consider carefully the implications regarding which normative system is most appropriate for specific types of evaluations.

An investigation of methods to detect feigned reading disabilities.

No clinically proven method currently exists to determine if a test taker is feigning or exaggerating symptoms of a specific reading disability (RD) for potential secondary gain (i.e., extra time on examinations, access to bursary funds, or tax benefits). Our objective was to examine the utility of previously proposed symptom validity measures (i.e., the Dyslexia Assessment of Simulation or Honesty [DASH] and the resulting Feigning Index [FI]) in discriminating students with genuine RDs from sophisticated simulators given ample time to prepare, who were warned that noncredible performance could be detected. The DASH correctly classified almost 83% of coached simulators with no false positives. The FI accurately classified 86% of post-secondary students feigning RD without misidentifying any students with a genuine RD, resulting in 91.8% overall classification accuracy. These two methods show promise as a means of detecting noncredible performance in the assessment of RD.

Waiting for a hand: saccadic reaction time increases in proportion to hand reaction time when reaching under a visuomotor reversal

Although eye movement onset typically precedes hand movement onset when reaching to targets presented in peripheral vision, arm motor commands appear to be issued at around the same time, and possibly in advance, of eye motor commands. A fundamental question, therefore, is whether eye movement initiation is linked or yoked to hand movement. We addressed this issue by having participants reach to targets after adapting to a visuomotor reversal (or 180° rotation) between the position of the unseen hand and the position of a cursor controlled by the hand. We asked whether this reversal, which we expected to increase hand reaction time (HRT), would also increase saccadic reaction time (SRT). As predicted, when moving the cursor to targets under the reversal, HRT increased in all participants. SRT also increased in all but one participant, even though the task for the eyes—shifting gaze to the target—was unaltered by the reversal of hand position feedback. Moreover, the effects of the reversal on SRT and HRT were positively correlated across participants; those who exhibited the greatest increases in HRT also showed the greatest increases in SRT. These results indicate that the mechanisms underlying the initiation of eye and hand movements are linked. In particular, the results suggest that the initiation of an eye movement to a manual target depends, at least in part, on the specification of hand movement.

Implications for Educational Classification and Psychological Diagnoses Using the Wechsler Adult Intelligence Scale–Fourth Edition With Canadian Versus American Norms

Building on a recent work of Harrison, Armstrong, Harrison, Iverson and Lange which suggested that Wechsler Adult Intelligence Scale–Fourth Edition (WAIS-IV) scores might systematically overestimate the severity of intellectual impairments if Canadian norms are used, the present study examined differences between Canadian and American derived WAIS-IV scores from 861 postsecondary students attending school across the province of Ontario, Canada. This broader data set confirmed a trend whereby individuals’ raw scores systematically produced lower standardized scores through the use of Canadian as opposed to American norms. The differences do not appear to be due to cultural, educational, or population differences, as participants acted as their own controls. The ramifications of utilizing the different norms were examined with regard to psychoeducational assessments and educational placement decisions particularly with respect to the diagnoses of Learning Disability and Intellectual Disability.