Gap Task Research Articles

Neural correlates of inter- and intra-individual saccadic reaction time differences in the gap/overlap paradigm

To examine the neural correlates of contextually differing control mechanisms in saccade initiation, we studied 18 subjects who performed two saccade paradigms in a pseudo-random order, while their eye movements were recorded in the MRI scanner (1.5 T). In the gap task the fixation point was extinguished 200 ms before target onset, and in the overlap task the fixation point vanished 500 ms after target onset. Subjects were asked to maintain stable fixation in the fixation period and to quickly saccade to peripherally presented targets. Inter-individual activation differences were assessed using regression analyses at the second level, with mean saccadic reaction time (SRT) of subjects as a covariate. To identify brain regions varying with trial-by-trial changes in SRTs, we included SRTs as a parametric modulation regressor in the general linear model. All analyses were regions of interest based and were performed separately for the gap and overlap conditions. For the gap paradigm, we did not obtain activation in regions previously shown to be involved in preparatory processes with much longer gap periods. Interestingly, both inter- and intra-individual variability analyses revealed a positive correlation of activation in frontal and parietal eye-movement regions with SRTs, indicating that slower saccade performance is possibly associated with higher cortical control. For the overlap paradigm, the trial-by-trial variability analysis revealed a positive correlation of activation in the right opercular inferior frontal gyrus with SRTs, possibly linked to fixation-related processes that have to be overcome to perform a speeded saccade in presence of a fixation point.

Analysis: UN goals need business backing

Technology and private-sector funding will drive progress towards the UN's ambitious development goals. The United Nations summit on the Millennium Development Goals (MDGs) confirmed one important aspect of their viability that was probably tacitly understood. Achieving the ambitious programme within its 2015 deadline will require an increasing contribution from the private sector. The MDG Gap Task Force revealed that overall UN funding will be $20bn short this year alone, with African nations struggling the most and falling $16bn below their original commitments. It also noted that among developed nations, only Belgium and the UK had committed to keep their payments at previously announced levels. But when the concrete details of implementing the eight MDGs are reviewed, the UN's promoter role gives way to the action being achieved through such private-sector groups as the UN Foundation (originally set up with a $1 bn grant from broadcasting mogul Ted Turner) and the Clinton Global Initiative (established by former US President Bill Clinton). Both those organisations held major meetings in New York alongside the opening of the UN General Assembly and had sessions specifically addressing what technology can do in the context of the MDGs. Kathy Calvin, the UN Foundation's CEO, is putting major effort into Goals Four, Five and Six through the $30m mHealth scheme set up with, among others, Vodafone. As its name suggests this addresses the use of mobile communications to improve public healthcare. 'When health workers were going out on vaccination campaigns or were tracking outbreaks of diseases or tracking stock-outs of commodities, such as condoms, they would typically write it down on a piece of paper and send it someplace. And maybe three months later, it would be noted,' she told FrontLines, in-house publication for the USAID development agency. 'Now, they're using handheld devices; in some cases, cellular phones. Even in the poorest of regions, mobile phones are prevalent. So that turned out to be a really tremendous leap for the World Health Organisation and other health workers. 'That led us to realise that there are many obstacles to wide-scale adoption of mobile technology for a broad array of health uses, whether they be diagnostic or reminders about taking drugs or data collection.' Mobile phones represent the only form of Internet connectivity in remote villages still to receive electricity, never mind landline phones. This feeds into the wider issue of how wireless comms can advance all the MDGs by fostering economic growth (e.g., making it easier for farmers to get the right crops to the right markets), improving education (e.g., enabling distance learning) and so on. A panel at the Clinton Global Initiative heard about this theme from figures as diverse as Cisco Systems CEO John Chambers and Ory Okolloh, one of the founders of the Ushahidi networking site being used in Haiti and Pakistan to assist crisis management. Chambers identified the importance of public-private partnerships specifically. He said the objective needed to be 'addressing the have-nots in the world at a much faster pace,' and doing this with both wired and wireless networks that users could afford. He also discussed how developing countries could 'skip a generation' and deploy the latest technologies more efficiently without incurring legacy costs seen in the West. Okolloh described how open source technologies such as Ushahidi can sit on top of such infrastructure to make services and tools easier to develop and distribute. 'Centres of innovation are not just in Silicon Valley today,' she said. 'This is a technology that was born in Kenya. We don't just consume technology now; we can produce it.' She argued for a need to move beyond handsets towards low-cost tablets. 'You want the $100 iPad,'she said, stressing that these would be more viable not only for sophisticated healthcare applications but also education. The UN itself though really put the stamp on how the private sector could couple with the almost Moore's Law-driven approach to using technology, implicit the visions of Okolloh, Chambers and Calvin. It did so by formally giving private-sector players a role in the MDG programme equal to that of nation states, by issuing a donor statement backed by UN secretary general Ban Ki-moon. 'Rather than viewing the private sector merely as resource providers, we choose to recognise the private sector as equal partners around key development issues and will enter into partnerships with local and international companies of various sizes,' the statement says. 'We aim to collaborate with companies that focus not only on profit margin, but also on social and environmental impact, and whose work harmonises with our developmental goals.'.

The time course of attentional disengagement from angry faces in social anxiety

While impaired attentional disengagement from threatening stimuli is thought to enhance social anxiety, it is unclear when the impaired disengagement occurs accurately. We used a gap task (Experiment 1) and an overlap task (Experiment 2) to reveal the impaired attentional disengagement from angry faces in socially anxious people with non-treatment seeking undergraduates. High ( N = 17 in Experiments 1 and 2) and low socially anxious people ( N = 17 in Experiment 1 and 19 in Experiment 2) were asked to fixate on an angry or neutral face presented at the center of a screen. Then, they discriminated the peripheral target stimuli. When there was a temporal gap between the face and target in Experiment 1 (gap task), the reaction times (RTs) for angry and neutral faces did not differ for all participants. However, when there was no gap and the face continued to appear in Experiment 2 (overlap task), the RTs for angry faces in high socially anxious people were longer than those for neutral faces after presentation times of 300 ms or longer. In low socially anxious people, the RTs following the angry and neutral faces did not differ. These results suggest that high socially anxious people face difficulty in disengaging attention from angry faces after recognizing them.

The influence of a visuomotor set on express saccades: Coordinate frames and contingency

Express saccades are the shortest latency eye movements known (70–110ms). However, previous work in our lab has shown that when elicited by the appearance of a spatially extended visual stimulus, express saccades have vectors influenced by a visuomotor set. In this case, the visuomotor set was established by an instruction to make a saccade to the left or right side of the stimulus array (Edelman et al, 2007). Remarkably, such a spatial “Cartesian instruction” does not increase saccade latency. Here, we extend these experiments in two ways. First, we examined whether a visuomotor set expressed in polar coordinates, established by an instruction to make a saccade to the nearer or farther of two visual stimuli arranged along an isodirectional line, is as effective as an instruction expressed in Cartesian coordinates. Second, we examined whether Cartesian instructions are effective when they are contingent, such that, for example, saccades are instructed to be made to the leftmost of two spots of light separated horizontally if they appear in the upper visual field and to the rightmost spot if they appear in the lower visual field. Subjects viewed a CRT display controlled by Vision Shell software routines while eye position was monitored by videooculography at 500 frames/s (Eyelink II, SR Research). A traditional gap task (gap duration: 150–200 ms) was used to facilitate express saccade production. First, we found that a visuomotor set established by a polar coordinate instruction influenced express saccade vector almost as much as Cartesian instructions, though there was a strong bias to make a saccade to the closer of the two targets. Second, we found that contingent Cartesian instructions had much less of an effect on saccade vector as non-contingent Cartesian instructions.

The effects of bottom-up target luminance and top-down spatial target predictability on saccadic reaction times

Saccadic reaction times (SRT) are composed of the sum of multiple processes, including bottom-up sensory processing, top-down goal oriented processing, and afferent and efferent conduction delays. In order to determine the timing dependencies and potential interactions between bottom-up and top-down processes on SRTs, we trained monkeys to perform several variants of visually guided saccade tasks. Bottom-up components of SRT were manipulated by varying target luminance from near detection threshold to supra-threshold ranges (i.e., 0.001-42.5 cd/m(2)). There was a significant reduction of mean SRT with increases in target luminance up to 3.5-17.5 cd/m(2). Luminance increases above these ranges produced significant increases in SRT when the target was within 6 degrees from the fovea. Top-down components were assessed by manipulating spatial target predictability across blocks of trials using either 1, 2, 4 or 8 possible target locations. Decreasing spatial target predictability increased SRT across target luminances from 1 to 4 targets in the gap task, but then paradoxically decreased SRT again when there were 8 possible targets in both the gap and step tasks. Finally, a gap task (200 ms gap) was used to determine the dependence of target luminance on the magnitude of the gap effect. Decreasing target luminance significantly reduced the magnitude of the gap effect indicating that the gap effect is strongly influenced by bottom-up factors.

Auditory processing in children with language-based learning problems: a magnetencephalography study

We examined basic auditory temporal processing in children with language-based learning problems (LPs) applying magnetencephalography. Auditory-evoked fields of 43 children (27 LP, 16 controls) were recorded while passively listening to 100-ms white noise bursts with temporal gaps of 3, 6, 10 and 30 ms inserted after 5 or 50 ms. The P1m was evaluated by spatio-temporal source analysis. Psychophysical gap-detection thresholds were obtained for the same participants. Thirty-two percent of the LP children were not able to perform the early gap psychoacoustic task. In addition, LP children displayed a significant delay of the P1m during the early gap task. These findings provide evidence for a diminished neuronal representation of short auditory stimuli in the primary auditory cortex of LP children.

Switching between gap and overlap pro-saccades: cost or benefit?

Triggering of saccades depends on the task: in the gap task, fixation point switches off and target appears after a gap period; in the overlap task, target appears while fixation point is still on. Saccade latencies are shorter in the gap task, due to fixation disengagement and advanced movement preparation during the gap. The two modes of initiation are also hypothesized to be subtended by different cortical-subcortical circuits. This study tested whether interleaving the two tasks modifies latencies, due to switching between different modes of triggering. Two groups of healthy participants (21-29 vs. 39-55 years) made horizontal and vertical saccades in gap, overlap, and mixed tasks; saccades were recorded with the Eyelink. Both groups showed shorter latencies in the gap task, i.e. a robust gap effect and systematic differences between directions. For young adults, interleaving tasks made the latencies shorter or longer depending on direction, while for middle-age adults, latencies became longer for all directions. Our observations can be explained in the context of models such as that of Brown et al. (Neural Netw 17:471-510, 2004), which proposed that different combinations of frontal eye field (FEF) layers, interacting with cortico-subcortical areas, control saccade triggering in gap and overlap trials. Moreover, we suggest that in early adulthood, the FEF is functioning optimally; frequent changes of activity in the FEF can be beneficial, leading to shorter latencies, at least for some directions. However, for middle-age adults, frequent changes of activity of a less optimally functioning FEF can be time consuming. Studying the alternation of gap and overlap tasks provides a fine tool to explore development, aging and disease.

Exchanging Missing Information in Tasks: Old and New Interpretations

Information gap tasks have played a key role in applied linguistics (Pica, 2005). For example, extensive research has been conducted using information gap tasks to elicit second language data. Yet, despite their prominent role in research and pedagogy, there is still much to be investigated with regard to what information gap tasks offer research on second language learning and use. Do both participants in information gap tasks have the same participatory responsibilities and rights? How are these responsibilities and rights managed and co‐constructed? This article answers these questions by investigating the issue of information distribution and the interactional roles that manifest during the completion of information gap tasks. Using conversation analysis, the findings show how information gap tasks create specific interactional roles that result in specific interactional constraints. For example, the task design characteristic of exchanging referential information forms the basis of a two‐part interaction sequence, where the recipient of missing information is predisposed to expose problematic utterances. It is then argued that these findings can be used to improve the design and implementation of tasks for both pedagogical and empirical purposes.

Rare express saccades in elderly fallers

To examine horizontal saccades in elderly subjects with falling history; prior extensive screening was done to recruit subjects with falling history in the absence of pathology. Twelve elderly with falling history were tested. Two testing conditions were used: the gap (fixation target extinguishes prior to target onset) and the overlap (fixation stays on after target onset) paradigms. Each condition was run at three viewing distances--20 cm, 40 cm, and 150 cm, corresponding to convergence angle at 17.1 degrees, 8.6 degrees, and 2.3 degrees, respectively. Eye movements were recorded with the photoelectric IRIS (Skalar medical). (i) like in healthy elderly subjects, elderly with falling history produce shorter latencies in the gap paradigm than in the overlap paradigm; (ii) their latencies are shorter at near distances (20 and 40 cm) relative to 150 cm for both paradigms; (iii) the novel result is that they fail to produce express latencies even in the conditions (near viewing distance and the gap task) known to promote high rates of express in adults (25%) or in healthy elderly (20%). Seven from the 10 healthy elderly produced express saccades at rates >12%, while 9 of the 12 older subjects with falling history showed no express saccades at all; the remaining 3 subjects showed low rates <12%. The quasi paucity of express saccades could be due to the disequilibrium of complex cortical/subcortical networks needed for making express saccades. The results support models suggesting specific network for express saccades; missing of such optomotor reflex may go along with missing other reflexes as well increasing the chances of falling.

Dual LATER-unit model predicts saccadic reaction time distributions in gap, step and appearance tasks

Saccadic latencies have long been known to depend on the relative timing of the appearance of the new target, and offset of the original fixation target. Previous studies have tended to conclude that two separate effects are at work, one equivalent to competitive inhibition from the fixation target, and the other due to its offset providing a warning that shortens latency. In this study, we propose a simpler explanation, based on a well-established model of reaction time, LATER (linear approach to threshold with ergodic rate), that in addition to predicting mean latencies also--more challengingly--predicts latency distributions. We show that observed distributions, using gap, step and appearance tasks under three conditions of prior probability, can be accurately predicted by using a pair of LATER units, one corresponding to fixation target offset and the other to peripheral target onset. Because fixation offset is probabilistically associated with target appearance, when the fixation unit is activated it increases the target's decision signal (that represents probability) in a fixed proportion, speeding responses. In contrast, when the fixation target remains present, the fixation unit is not activated, and responses are slower. Both these effects generate characteristic changes in the shapes of the latency distributions that can be accurately predicted by the model.

Prior information and oculomotor initiation: the effect of cues in gaps

Eye movements reflect not only an important output of various neural control systems, but also often reflect cognitive processing. For example, saccades are frequently used as a behavioural index of attentional processing. A second important eye movement type, smooth pursuit (SP), has received much less attention in this regard. These two types of eye movement were classically thought of as being separate, but recent results have suggested a closer linkage of their control mechanisms and perhaps their interactions with cognitive processes. Prior information, in the form of cues, alters saccade latency leading to characteristic cueing effects. When the period between the appearance of the cue and the appearance of the saccade target is sufficiently long, the latency of saccades to targets appearing at cued locations is increased. This "inhibition of return" is enhanced by a second type of stimulus manipulation, the early removal of the fixation target a few hundred milliseconds before the target appears (the gap paradigm). In the current experiments, the effect of cues, and interactions between cues and long gaps were investigated. In the main pursuit experiment, and in a separate saccade experiment, subjects were presented with interleaved runs of tasks with and without long gaps (gap duration = 1 s), and with and without cues. In tasks without cues, SP latency was reduced by long gaps (mean reduction 8 ms); unexpectedly, saccade latency for non-cue tasks was increased by long gaps (mean increase 41 ms). In a control experiment with only non-cue tasks, in which SP and saccade gap and non-gap tasks were run together, SP latency was again reduced in gap tasks, while saccade latency was increased, but by much less than in the first experiment. Analysis of individual subjects' data showed that while gaps increased saccade latency in two subjects who had participated in the main experiment (in which cues and gaps had been combined), in two naive subjects long gaps did not affect saccade latency. In the main pursuit experiment, cues had both spatially specific and non-spatially specific (warning) effects on pursuit latency. In non-gap conditions, latency was greater when contralateral cues were presented 250 ms prior to the appearance of the pursuit target, compared to ipsilateral cues, a pattern of effect consistent with inhibition of return. However, this was reversed when cues appeared during a gap--contralateral cues increased while ipsilateral cues decreased latency. For saccades, as expected, in both gap and non-gap conditions, cue effects were consistent with inhibition of return (latency was lower with contralateral cues), and the inhibition of return effect was larger in gap, compared to non-gap conditions. The results suggest that, in appropriate contexts (or as a result of appropriate training), there are distinct inhibitory mechanisms that operate on saccades but not pursuit. What appears to be an inhibition of return effect on pursuit latency when static cues are presented in pursuit tasks, may be better understood as the product of a modulation of mechanisms active in pursuit initiation, perhaps related to motion processing. In contrast to some recent evidence suggesting a close anatomical and functional linkage between pursuit and saccade initiation, the results are consistent with the involvement of a wider range of mechanisms, or a greater degree of flexibility, in programming the initiation of these two oculomotor behaviours.

On the limited role of target onset in the gap task: Support for the motor-preparation hypothesis

Saccade latency is reduced when the fixation stimulus is removed shortly before a saccade target appears (gap task) as compared to when the fixation stimulus remains present (overlap task). To test the assumption that this gap effect benefits from advanced motor preparation (M. Paré & D. P. Munoz, 1996), we manipulated target onset independently of the signal to launch a saccade (peripheral offset at the mirror location). In Experiment 1, we showed that, when the target appears at one of only two possible locations, target onset strongly improves performance (lower latency, higher accuracy) in the overlap task but not in the gap task. In Experiment 2, we found that the lack of an effect of target onset in the gap task was not due to inhibition of a reflexive response to the transient associated with the offset (go signal) in our task. In Experiment 3, we manipulated target onset and target uncertainty (two, four, or eight potential target locations) in gap and overlap tasks. As target uncertainty increased, the gap effect decreased, and the effect of target onset on saccade latency in the gap condition became greater. Overall, our results suggest, in line with the motor-preparation hypothesis, that saccade metrics in a gap task are computed before the target is actually displayed and that advanced motor preparation is enhanced when the location of the target is predictable. Analyses of anticipations and regular-latency errors corroborated this view.

Effects of thirty-minute mobile phone exposure on saccades

Objective To investigate whether exposure to pulsed high-frequency electromagnetic field (pulsed EMF) emitted by a mobile phone has short-term effects on saccade performances. Methods A double blind, counterbalanced crossover design was employed. In 10 normal subjects, we studied the performance of visually guided saccade (VGS), gap saccade (GAP), and memory guided saccade (MGS) tasks before and after exposure to EMF emitted by a mobile phone for thirty minutes or sham exposure. We also implemented a hand reaction time (RT) task in response to a visual signal. Results With the exception of VGS and MGS latencies, the parameters of VGS, GAP and MGS tasks were unchanged before and after real or sham EMF exposure. In addition, the latencies of VGS and MGS did not change differently after real and sham exposure. The hand RT shortened with the repetition of trials, but again this trend was of similar magnitude for real and sham exposures. Conclusions Thirty minutes of mobile phone exposure has no significant short-term effect on saccade performances. Significance This is the first study to investigate saccade performance in relation to mobile phone exposure. No significant effect of mobile phone use was demonstrated on the performance of various saccade tasks, suggesting that the cortical processing for saccades and attention is not affected by exposure to EMF emitted by a mobile phone.

Language learning

Language learning

Aging does not affect the accuracy of vertical saccades nor the quality of their binocular coordination: A study of a special elderly group

Fine binocular coordination of vertical saccades is a complex process requiring appropriate distribution of innervations to all six extraocular muscles. Loss of such coordination causes vertical binocular disparities that are particularly bothersome. We studied the quality of binocular control of vertical saccades in healthy subjects, 11 young adults (20–28 years) and 11 elderly adults (63–75 years). We used LED targets at 7.5° or 15° from the center (fixation), up or down in four conditions: gap and overlap tasks, each done at two distances—near (40 cm) and far (150 cm). Vertical eye movements were recorded with video-oculography (CHRONOS). The results showed: aged subjects performed vertical saccades as accurately as young subjects. Importantly, the binocular coordination of vertical saccades was well preserved in the elderly; the mean difference of vertical saccades between the two eyes was 0.10° and 0.09° in young and elderly subjects, respectively. Upward saccades were associated with divergence, downward ones with convergence. This secondary phenomenon was also the same and of the similar amplitude for young (1.30°) and elderly (1.25°) subjects. Thus, despite its complexity, the quality of binocular coordination of vertical saccades remains intact with age. The other observations are mostly dependent of several aspects on the direction (up/down), viewing distances and eccentricities; the horizontal vergence during or after vertical saccades was found to be larger for downward saccades than for upward saccades, for saccades at far distance than at close, and for the more eccentric targets (15° versus 7.5°). All these phenomena are the same for both young and elderly subjects. We conclude that the accuracy and the binocular coordination of vertical saccades, at least for target steps less than 15°, are preserved in elderly subjects <75 years who maintain good physical and intellectual form. The data are consistent with the idea of the existence of non-aging system function in the human CNS.

Language learning

Language learning

INFORMATION GAP TASKS: Their Multiple Roles and Contributions to Interaction Research Methodology

This article describes how information gap tasks can be designed as instruments for data collection and analysis and as treatments in interaction research. The development of such tasks is illustrated and data are presented on their role in drawing learners' attention to second language (L2) forms that are difficult to notice through classroom discussion alone. Because the tasks presented here are closed-ended and precision oriented and require the exchange of uniquely held information, they promote modified interaction among participants and orient their attention to form, function, and meaning. These processes can be observed by the researcher during task implementation. Thus, the tasks reduce researcher dependence on externally applied treatments and analytical instruments not integral to the interaction itself. To illustrate this methodology in use, we report on a study in which six pairs of intermediate-level English L2 learners carried out three types of information gap tasks in their classrooms. They first read passages on familiar topics, whose sentences contained L2 forms that were low in salience and difficult to master but developmentally appropriate. To complete the tasks, the learners were required to identify, recall, and compare the forms, their functions, and their meanings. Data revealed close relationships among learners' attentional processes, their recall of form, function, and meaning, and the interactional processes that supported their efforts.In carrying out the design and implementation of the tasks in this article, we have worked most closely with Kristine Billmyer and MaryAnn Julian, and also Jin Ahn, Marni Baker-Stein, Mara Blake-Ward, Lyn Buchheit, Junko Hondo, Sharon Nicolary, and Jack Sullivan. Among the many graduate students who have provided assistance are Vivian Chen, Yao Chen, Yi-Chen Chen, Cathy Fillman, Leslie Harsch, Hanae Katayana, Ji Hwan Kim, Atsuko Matsui, Lisa Mullen, Amy Nichols, Matthew Salvatore, Margaret Skaarup, Lauren Smith, Cheng-Chen Tseng, Debbie Tsui, Melissa Yi, Wei-Chieh Yu, and Mira Yun.

Temporal processing deficits in the pre-senescent auditory system

This study tested the hypothesis that temporal processing deficits are evident in the pre-senescent (middle-aged) auditory system for listening tasks that involve brief stimuli, across-frequency-channel processing, and/or significant processing loads. A gap duration discrimination (GDD) task was employed that used either fixed-duration gap markers (experiment 1) or random-duration markers (experiment 2). Independent variables included standard gap duration (0, 35, and 250 ms), marker frequency (within- and across-frequency), and task complexity. A total of 18 young and 23 middle-aged listeners with normal hearing participated in the GDD experiments. Middle age was defined operationally as 40-55 years of age. The results indicated that middle-aged listeners performed more poorly than the young listeners in general, and that this deficit was sometimes, but not always, exacerbated by increases in task complexity. A third experiment employed a categorical perception task that measured the gap duration associated with a perceptual boundary. The results from 12 young and 12 middle-aged listeners with normal hearing indicated that the categorical boundary was associated with shorter gaps in the young listeners. The results of these experiments indicate that temporal processing deficits can be observed relatively early in the aging process, and are evident in middle age.

L2 Tasks and Orientation to Form

AbstractTask-based language teaching has been advocated as a means of promoting learning through learner interactions in the classroom. However, characteristics of the design and implementation of communicative tasks have been shown to influence learner orientation to form. One task characteristic that may affect learner attention to form, modality, is examined here to determine whether it influences learners' tendency to focus on second language form. Forty-four adult ESL learners engaged in information gap tasks targeted at specific second language forms that required the learners to collaboratively achieve both an oral and a written outcome. Analysis of orientation to form in both spoken and written sections of the task indicated that task modality plays a role in influencing learner orientation to form.

The control of vertical saccades in aged subjects

In real life we produce vertical saccades at different distances and eccentricities, and while our fixation is more or less actively engaged. The goal of this study is to examine vertical saccades in aged and young subjects, taking into consideration all these parameters. Eleven adults (20-28 years) and 11 aged subjects (63-83 years) were recruited. We used LED targets at 7.5 degrees or 15 degrees, up or down in four conditions: gap and overlap tasks, each done at two distances-at near (40 cm) and at far (150 cm). In the gap task fixation target extinguishes prior to target onset, while in the overlap condition it stays on after target onset; consequently, visual attention and fixation are employed differently in the two tasks. Eye movements were recorded with the Chronos video eye tracker. Results showed that vertical saccades were longer for aged subjects than for young adults under almost all conditions. For both aged and young subjects, latencies were shorter under the gap than under the overlap task. Latencies for eccentric targets at 15 degrees were significantly longer than those at 7.5 degrees but for aged subjects only; this effect was more pronounced for upward saccades under the overlap condition. Express type of latencies (80-120 ms) occurred frequently in the gap task and at similar rates for young adults (16%) and aged subjects (12%); in the overlap task express latencies were scarce in young adults (0.4%) and aged subjects (1.8%). Age deteriorates the ability to trigger regular volitional saccades but not the ability to produce express type of saccades. Latency increase with aging is attributed to the degeneration of central areas, e.g. oculomotor cortical areas involved in the initiation of vertical saccades.