Saccadic eye movements as indicators of cognitive function in older adults

Older adults appear to have greater difficulty ignoring distractions during day-to-day activities than younger adults. To assess these effects of age, the ability of adults aged between 50 and 80 years to ignore distracting stimuli was measured using the antisaccade and oculomotor capture tasks. In the antisaccade task, observers are instructed to look away from a visual cue, whereas in the oculomotor capture task, observers are instructed to look toward a colored singleton in the presence of a concurrent onset distractor. Index scores of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) were compared with capture errors, and with prosaccade errors on the antisaccade task. A higher percentage of capture errors were made on the oculomotor capture tasks by the older members of the cohort compared to the younger members. There was a weak relationship between the attention index and capture errors, but the visuospatial/constructional index was the strongest predictor of prosaccade error rate in the antisaccade task. The saccade reaction times (SRTs) of correct initial saccades in the oculomotor capture task were poorly correlated with age, and with the neurospsychological tests, but prosaccade SRTs in both tasks moderately correlated with antisaccade error rate. These results were interpreted in terms of a competitive integration (or race) model. Any variable that reduces the strength of the top-down neural signal to produce a voluntary saccade, or that increases saccade speed, will enhance the likelihood that a reflexive saccade to a stimulus with an abrupt onset will occur.     

Lateral information transfer across saccadic eye movements

Our perception of the visual world remains stable and continuous despite the disruptions caused by retinal image displacements during saccadic eye movements. The problem of visual stability is closely related to the question of whether information is transferred across such eye movements-and if so, what sort of information is transferred. We report experiments carried out to investigate how presaccadic signals at the location of the saccade goal influence the visibility of postsaccadic test signals presented at the fovea. The signals were Landolt rings of differ-ent orientations. If the orientations of pre- and postsaccadic Landolt rings were different, the thresholds of the test signals were elevated by about 20%–25% relative to those at the static control condition. When the orientations were identical, no such elevation occurred. This selective threshold elevation effect proved to be a phenomenon different from ordinary saccadic suppression, although it was closely related to the execution of the saccadic eye movement. The consequences for visual stability are discussed.     

Information processing during saccadic eye movements

Saccadic eye movements are made at least 100,000 times each day. It is well known that sensitivity to visual input is suppressed during saccades; recent evidence suggests that some kinds of information processing are suppressed as well. Suppression during saccades implies that processing occurs discretely (during eye fixations only), rather than continuously (during both fixations and saccades). We examined this issue in the context of the Posner and Snyder (1975) primed letter-matching task. We found that a prime viewed in one fixation had a larger influence on targets viewed in a second fixation when a long rather than a short saccade separated the two fixations. This result demonstrates that at least some information processing occurs during saccades.     

Visuospatial perceptual sequence learning and eye movements

We examined perceptual sequence learning by means of an adapted serial reaction time task in which eye movements were unnecessary for performing the sequence learning task. Participants had to respond to the identity of a target letter pair ("OX" or "XO") appearing in one of four locations. On the other locations, similar distractor letter pairs ("QY" or "YQ") were shown. While target identity changed randomly, target location was structured according to a deterministic sequence. To render eye movements superfluous, (1) stimulus letter pairs appeared around a fixation cross with a visual angle of 0.63°, which means that they appeared within the foveal visual area and (2) the letter pairs were presented for only 100 ms, a period too short to allow proper eye movements. Reliable sequence knowledge was acquired under these conditions, as responses were both slower and less accurate when the trained sequence was replaced by an untrained sequence. These results support the notion that perceptual sequence learning can be based on shifts of attention without overt oculomotor movements.     

The role of eye movements in motor sequence learning

An experiment that utilized a 16-element movement sequence was designed to determine the impact of eye movements on sequence learning. The participants were randomly assigned to two experimental groups: a group that was permitted to use eye movements (FREE) and a second group (FIX) that was instructed to fixate on a marker during acquisition (ACQ). A retention test (RET) was designed to provide a measure of learning, and two transfer tests were designed to determine the extent to which eye movements influenced sequence learning. The results demonstrated that both groups decreased the response time to produce the sequence, but the participants in the FREE group performed the sequence more quickly than participants of the FIX group during the ACQ, RET and the two transfer tests. Furthermore, continuous visual control of response execution was reduced over the course of learning. The results of the transfer tests indicated that oculomotor information regarding the sequence can be stored in memory and enhances response production.     

Inhibition of attended processing during saccadic eye movements

People are unable to perform some, but not all, cognitive tasks while moving their eyes. A possible common denominator among disrupted processes is the use of attention. The present research proposes and tests an attentional suppression hypothesis to evaluate this claim. This hypothesis states that because attention is obligatorily allocated to a to-be-fixated location prior to the onset of a saccade, during saccadic events attentional resources are unavailable to direct processing associated with higher order cognitive tasks. Subjects were engaged in a task that combined saccades and shifts of attention across global and local levels of hierarchical figures. When the eyes did not move, this shift took place between stimulus presentations. When saccades intervened between the stimuli, the global-local shifts of attention were interrupted, suggesting that saccades suppress cognitive processes requiring attention.     

Response selection in paired-associate learning

Ss were presented pairs of items on study cycles; on test cycles Ss were presented the stimulus items and required either to recall the correct response or to indicate the correct response from three alternatives. It was demonstrated that Ss who chose the correct responses from the alternatives tended to select from both stimulus and response compounds so that the association was between stimulus and response components. The amount of selection from the response compounds was comparable to that from the stimulus compounds.     

Enactive imagery in paired-associate learning

Three experiments were conducted to study the effects of enactive imagery (EI) on associative learning. In Experiment I, groups of Ss rated 226 verbs on EI and frequency. In Experiments II and III, Ss learned a 24- and a 16-item list, respectively. The lists consisted of the four possible stimulus-response combinations of high (H) and low (L) EI verb pairs: H-H, H-L, L-H, L-L. In both experiments, EI was found to be a significant factor on the stimulus side, performance being superior when the stimulus was of high EI. In Experiment III, the response EI main effect and the Stimulus by Response EI interaction were also found to be significant. The results indicated that like the imagery evoked by nouns, the EI evoked by verbs facilitates learning.     

Second responses in paired-associate learning

Mathematical models of memory can be evaluated using a continuous paired-associate learning paradigm in which a second response is requested immediately following an error. This procedure provides discriminability among the models on the basis of the relationship between the first- and second-response error probabilities. Theoretical predictions are derived for a variety of models, including finite-state and noncontingent operator models, formulations based on the theory of signal detectability, the multicomponent memory model of Bower (1967b), and the long- and short-term model of Atkinson and Shiffrin (1968). None of these is unequivocally acceptable, and many are decisively rejected by the data of a single-trial experiment. The most satisfactory models are the multicomponent model and the Atkinson and Shiffrin model, both of which assume a greater degree of internal structure than the rejected models. It appears that internal structure of this sort will be a necessary part of any satisfactory model of second responses.