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To acquire something that we see, visual spatial information must ultimately result in the activation of the appropriate set of muscles. This sensory to motor transformation requires an interaction between information coding target location and information coding which effector will be moved. Activity in the monkey parietal reach region (PRR) reflects both spatial information and the effector (arm or eye) that will be used in an upcoming reach or saccade task. To further elucidate the functional role of PRR in visually guided movement tasks and to obtain evidence that PRR signals are used to drive arm movements, we tested the hypothesis that increased neuronal activity during a preparatory delay period would lead to faster reach reaction times but would not be correlated with saccade reaction times. This proved to be the case only when the type of movement and not the spatial goal of that movement was known in advance. The correlation was strongest in cells that showed significantly more activity on arm reach compared with saccade trials. No significant correlations were found during delay periods in which spatial information was provided in advance. These data support the idea that PRR constitutes a bottleneck in the processing of spatial information for an upcoming arm reach. The lack of a correlation with saccadic reaction time also supports the idea that PRR processing is effector specific, that is, it is involved in specifying targets for arm movements but not targets for eye movements.

Optimal vibration stimulation to the neck extensor muscles using hydraulic vibrators to shorten the saccadic reaction time was examined. Subjects were 14 healthy young adults. Visual targets (LEDs) were located 10 degrees left and right of a central point. The targets were alternately lit for random durations of 2-4 seconds in a resting neck condition and various vibration conditions, and saccadic reaction times were measured. Vibration amplitude was 0.5 mm in every condition. The upper trapezius muscles were vibrated at 40, 60, 80, and 100 Hz in a sub-maximum stretch condition in which the muscles were stretched at 70% of maximum stretch. In addition, the muscles were vibrated at 60 Hz with the muscles maximally stretched, with 70% vertical pressure without stretching, and with vibration applied to the skin in the same area as the muscle vibration. At 60, 80, and 100 Hz at 70% maximum stretch, saccadic reaction time shortened significantly compared with the resting neck condition. However, no significant difference in the reaction time was observed among the frequencies. The saccadic reaction times in the maximum stretch condition, muscle pressure condition, and skin contact condition did not differ significantly from that in the resting neck condition. Vibration stimulation to the trapezius with 60-100 Hz frequencies at 0.5 mm amplitude in the sub-maximum stretch condition was effective for shortening saccadic reaction time. The main mechanism appears to be Ia information originating from the muscle spindle.

Saccadic reaction time (SRT) was measured in a focused attention task with a visual target stimulus (LED) and auditory (white noise burst) and tactile (vibration applied to palm) stimuli presented as non-targets at five different onset times (SOAs) with respect to the target. Mean SRT was reduced (i) when the number of non-targets was increased and (ii) when target and non-targets were all presented in the same hemifield; (iii) this facilitation first increases and then decreases as the time point of presenting the non-targets is shifted from early to late relative to the target presentation. These results are consistent with the time-window-of-integration (TWIN) model (Colonius and Diederich in J Cogn Neurosci 16:1000-1009, 2004) which distinguishes a peripheral stage of independent sensory channels racing against each other from a second stage of neural integration of the input and preparation of an oculomotor response. Cross-modal interaction manifests itself in an increase or decrease of second stage processing time. For the first time, without making specific distributional assumptions on the processing times, TWIN is shown to yield numerical estimates for the facilitative effects of the number of non-targets and of the spatial configuration of target and non-targets. More generally, the TWIN model framework suggests that multisensory integration is a function of unimodal stimulus properties, like intensity, in the first stage and of cross-modal stimulus properties, like spatial disparity, in the second stage.

Purpose: This study evaluated hypothesis that the faster saccadic reaction time in professional clay-target shooters found in a previous study was because of a superiority of athletes arising at the attention level or at level of saccadic motor preparation. Method: Ten shooters with at least 6 yr of shooting training in Olympic shotgun disciplines and 10 control subjects participated in the experiments. In the first experiment, prosaccades were studied by comparing the saccadic latencies obtained from the overlap and gap paradigms. In the overlap paradigm, a target was presented randomly at one of four cardinal positions with the fixation point presented throughout the trial duration. In the gap paradigm, the fixation point was removed at the time of target presentation. In the second experiment, subjects were instructed to saccade as quickly as possible in the direction opposite to that of the target location (antisaccades). Results: Shooters had shorter saccadic latency than controls, both with gap and overlap conditions in the first experiment and in the antisaccade condition of the second experiment. Conclusion: This result indicates that athletes' advantage in saccadic reaction times cannot be attributed to improvement of the attentional mechanism of disengagement. Present results support the hypothesis that shooters develop shorter motor preparation to saccades.

Saccadic reaction time (SRT) of 4-, 6- and 8-month-old infants' was measured during tracking of abruptly changing trajectories, using a longitudinal design. SRTs decreased from 595 ms (SE=30) at 4 months of age to 442 ms (SE=13) at 8 months of age. In addition, SRTs were lower during high velocities (comparing 4.5 and 9 degrees/s) and vertical (compared to horizontal) saccades.

The anti-saccade task is an important tool for investigating both the generation of voluntary saccades and the suppression of involuntary, stimulus driven, saccades. In the anti-saccade task participants have to suppress an involuntary saccade to the stimulus in order to generate a voluntary saccade away from the stimulus. The extent to which errors occur in this task indicates the ability of the stimulus to trigger an orienting response that is beyond the control of the participant. Here we show an increase in anti-saccade error rates away from an upright face compared to a non-upright face. This suggests that complex high-level visual properties of the stimulus can influence whether involuntary orienting occurs.

Reaction time (RT) decreases with stimulus intensity. Hughes and Kesley (1984) demonstrated, however, that the effect of stimulus intensity on simple RT is larger for manual than for saccadic responses. We reexamined this relation under various conditions. The dissociation occurred when the task enabled the generation of exogenous saccades. We found, however, no dissociation if endogenous saccades had to be executed. It is hypothesized that the different effects of intensity result from the simplified neuronal processing of exogenous saccades performed in the direct route from the retina to the superior colliculus.

The time course of the process preparing for saccade eye movement was investigated in a psychophysical experiment involving a delayed saccade task. The presentation of the saccade response signal was delayed with respect to the presentation of a cue that informed the subject of metrics of the upcoming saccade. The cue appeared probabilistically at one of two potential locations. The saccadic reaction times (SRTs) decreased with longer delays of the saccade response signal. This indicates that the preparatory process of the saccade progresses according to the information about the metrics of the saccade during the delay. Additionally, the difference in saccade reaction times for different probabilities of the cue presentation disappeared with a delay longer than 192 ms. This suggests that the effect of the prediction according to the probability decreases as the preparatory process evoked by the cue progresses. We examined whether the data could be explained with a linear model.

Intraocular inflammatory eye disease is one of the important causes of ocular morbidity. Even though the prevalence of uveitis is less common in relation to diabetic retinopathy, glaucoma or age related macular degeneration, the complexity and heterogeneity of the disease makes it more unique. Putative uveitogenic retinal antigens incite innate immunity by the process of antigen mimicry and have been shown to be associated in patients with intraocular inflammatory disease by numerous experimental studies. Laboratory diagnostic tools to aid the etiologic association in intraocular inflammatory disease have evolved over the last two decades and we are entering into an era of molecular diagnostic tests. Sophisticated novel technologies such as multiplex bead assays to assess biological signatures have revolutionized the management of complex refractory uveitis. Nevertheless, there is still a long way to go to establish the causal relationship between these biomarkers and specific uveitic entities. Experimental studies have shown the supreme role of infliximab in the management of Behcet′s disease. Despite significant experimental and case control studies, the deficiency of randomized clinical trials using these biologic agents has handicapped us in exploring them as a front line therapy in severe refractory uveitis. Studies still need to answer the safety of these potentially life threatening drugs in a selected group of patients and determine when to commence and for how long the treatment has to be given. This review article covers some basic concepts of cytokines in uveitis and their potential application for therapy in refractory uveitis.

Background: With the advent of spectral domain optical coherence tomography (SDOCT), there has been a renewed interest in macular region for detection of glaucoma. However, most macular SDOCT parameters currently are thickness parameters which evaluate thinning of the macular layers but do not quantify the extent of area over which the thinning has occurred. We therefore calculated a new macular parameter, "ganglion cell complex surface abnormality ratio (GCC SAR)" that represented the surface area over which the macular thickness was decreased. Purpose: To evaluate the ability of SAR in detecting perimetric and preperimetric glaucoma. Design: Retrospective image analysis. Materials and Methods: 68 eyes with perimetric glaucoma, 62 eyes with preperimetric glaucoma and 165 control eyes underwent GCC imaging with SDOCT. SAR was calculated as the ratio of the abnormal to total area on the GCC significance map. Statistical Analysis: Diagnostic ability of SAR in glaucoma was compared against that of the standard parameters generated by the SDOCT software using area under receiver operating characteristic curves (AUC) and sensitivities at fixed specificities. Results: AUC of SAR (0.91) was statistically significantly better than that of GCC average thickness (0.86, P = 0.001) and GCC global loss volume (GLV; 0.88, P = 0.01) in differentiating perimetric glaucoma from control eyes. In differentiating preperimetric glaucoma from control eyes, AUC of SAR (0.72) was comparable to that of GCC average thickness (0.70, P > 0.05) and GLV (0.72, P > 0.05). Sensitivities at specificities of 80% and 95% of SAR were comparable (P > 0.05 for all comparisons) to that of GCC average thickness and GLV in diagnosing perimetric and preperimetric glaucoma. Conclusion: GCC SAR had a better ability to diagnose perimetric glaucoma compared to the SDOCT software provided global GCC parameters. However, in diagnosing preperimetric glaucoma, the ability of SAR was similar to that of software provided global GCC parameters.

Background: On the basis of the literature on autism, it was hypothesized that children with autism have deficits in attentional (dis-)engagement mechanisms. Methods: A saccadic gap-overlap task was used to study visual engagement and disengagement in 16 high-functioning autistic children of about 10 years of age and 15 age- and IQ-matched normal control children. Subjects were asked to make saccadic eye movements from a fixation point to a suddenly appearing target as fast as possible. The saccadic reaction time was compared in two conditions: 1) the overlap condition, in which the fixation point was continuously visible, and 2) the gap condition, in which the fixation point was turned off 200 msec before the target appeared. Results: Although no differences between the groups in either condition was observed, the gap effect (i.e., the difference in saccadic reaction time between the overlap condition and the gap condition) was smaller in the autistic group than in the control group. Conclusions: We concluded that autistic children show a lower level of attentional engagement.

Purpose: The saccadic reaction time (SRT) was measured as a saccadic movement parameter using visually guided tasks. Subjects and Method: The SRT was measured for nine healthy adult subjects aged from 28 to 49 years. The visually guided tasks for saccadic movement induction were simultaneous, gap, overlap, delayed-memory, and anti-SM tasks. Results: The median of the SRT (msec) for each task in the actual measurements was as follows: 216 for the simultaneous task, 180 for the gap task, 240 for the overlap task, 234 for the delayed-memory task, and 292 for the anti-SM task. The SRT distribution of each subject exhibited two peaks for the gap task but mostly one peak for each of the other tasks. The first peak, observed in the SRT distribution for the gap task was an eysress saccade. Conclusion: The SRT for the gap task was the shortest and the SRT got longer in the order of the simultaneous task, and the overlap task, and the anti-SM task. Some subjects easily showed an express saccade in the gap task, but others did not.

We investigated changes in saccadic reaction time in relation to the degree of increase in activity of neck extensor muscles when neck flexion occurred, and assessed the reliability of the measurements. Saccadic reaction time was measured firstly, during neck flexion angles set at 5 degrees increments from 0 degrees (resting position) to 25 degrees, with the chin either resting on a stand or not, and secondly, during shoulder girdle elevator muscles providing a relative muscle force of 30%, with the neck flexion angle maintained at 0 degrees by having the subjects rest their chins on a stand. Saccadic reaction time was evaluated by the latency to the beginning of eye movement toward the lateral target, which was moved at random intervals in 20 degrees amplitude jumps. Muscle activity in the trapezius muscle was evaluated using the mean amplitude of electromyogram recordings. Very high coefficients of reliability in muscle activity and saccadic reaction time were observed between the two sets of tests at 1-h intervals and also among the three trials with a 1-min rest. When their necks were flexed and the subjects rested their chins on a stand, muscle activity increased slightly in accordance with the enlargement of this angle, with no significant change in saccadic reaction time. With the chin not resting on the stand, muscle activity increased gradually, while the saccadic reaction time decreased to that obtained at an average neck flexion angle of 20 degrees. However, the angle where the shortest reaction time was obtained showed considerable individual variation (5-25 degrees ). Activity in the trapezius muscle at a 20 degrees neck flexion angle, with the chin not resting on the stand, was far less than that for 30% maximal voluntary contraction in shoulder girdle elevator muscles. Nevertheless, the saccadic reaction times were roughly equivalent under the two different sets of conditions. No sex differences were observed in terms of saccadic reaction time under any set of conditions.

Introducing a temporal gap between extinction of fixation point (FP) and occurrence of a visual target (T) is known to reduce the reaction time (RT) of saccades performed from FP to T. In this ‘gap paradigm’, as it is called, the frequency distribution of saccadic RTs is typically bimodal with an early peak of very short latency saccades (express sac-cades, ES) and a second peak of regular saccades (Fischer and Boch 1983). There are considerable inter-individual differences. A large proportion of ES has been taken to indicate a weak fixation system which normally inhibits the generation of reflexive saccades, a finding in a subpopulation of dyslexic children (Biscaldi et al. 1996). Moreover, repeated practice of this paradigm may increase the percentage of ES in some normal subjects. Also, target eccentricity plays a role (ES are missing with eccentricities

In an antisaccade-task subjects are required to look to the side opposite of a suddenly presented stimulus so that the voluntary and the reflexive components operate in opposite directions. In this study the gap-antisaccade- and the overlap-prosaccade-task were used to investigate the number of erroneous prosaccades in the antisaccade-task, their reaction times, and their correction times in relation to the number of express saccades a same subject produced in the overlap-prosaccade-task. Out of 234 subjects 126 were selected who produced more than 20 % errors. Among the data sets we differentiated between a “fast” group with many express saccades and a “slow” group with only a few express saccades in the overlap-prosaccade-task. Both groups showed differences in the reaction and correction time of their errors. In a second experiment we wanted to know whether the subjects (N=38) recognized their errors and whether a recognized sequence of an erroneous prosaccade and the corrective saccade is different from an unrecognized sequence. The results indicate that for each subject one has to differentiate between the disability to suppress reflex-like saccades due to an insufficient fixational control or due to a weak voluntary control or the disability to generate voluntary saccades. The erroneous prosaccades and their corrections escape the conscious perception in many cases despite large (4°+8°) and long lasting (>100 ms) changes of the retinal image. It is discussed that the perceptual spatial frame transforms differently prior to voluntary as compared to involuntary saccades.

It is well known that the removal of a fixation point prior to the presentation of a peripheral target dramatically reduces saccadic reaction time (SRT). This effect has become known as the "gap effect". The present study examined several detailed kinematic variables to determine whether the removal of the fixation point also affects the manner in which saccades are produced. The findings indicate that saccades that were initiated after the removal of the fixation point had higher average velocities and reached greater peak velocities, accelerations, and decelerations than did saccades produced in the presence of the fixation point. The results suggest that the removal of the fixation point may affect the force-time curves of saccades in addition to affecting the time needed to initiate the saccades.

When a temporal gap is introduced between the offset of the central fixation point and the appearance of a new target, saccadic reaction time is reduced (gap effect) and a special population of extremely fast saccades occurs (express saccades). It has been hypothesized that the gap triggers a readiness signal, which is responsible for the reduced saccadic reaction times. Here we recorded event-related potentials during the gap to in vestigate the central processes associated with the gener ation of fast regular saccades and express saccades. Prior to the execution of fast regular saccades, subjects pro duced a slow negative shift, with a maximum at frontal and central channels that started 40 ms after fixation offset. This widespread negativity is similar to a readiness potential. Anticipatory saccades were preceded by an increased frontal and parietal negativity. Prior to express saccades, a frontal negativity was observed, which started 135 ms after the disappearance of the fixation point. It is assumed that the frontal negativity prior to express saccades corresponds to the fixation-disengagement dis charge described in the frontal eye field of monkeys. Therefore, we hypothesize that fast regular saccades are the result of an increased readiness signal, while express saccades are the result of specific preparatory processes.

We studied predictive and pseudo random saccades in patients with cerebellopontine angle tumor. Target for the saccades was a laser beam which was reflected on the wall in front of the subject, and the stimulus was controlled by a computer. The fixed target was spaced at a distance of +/- 30 to each side of the subject. The random saccades jumped 20 degrees/40 degrees/60 degrees in an unpredictable manner. The saccade analysis program was based on pattern recognition. In the random saccade test none of the mean values of saccadic reaction time (SRT), saccadic accuracy (SA) and saccadic peak velocity (SPV) to the right or left differed significantly between the two groups. In the predictable saccade test there was statistically significant differences for certain variables: in right SRT (p0.01) and in left SRT (p0.01); in right SA (0.001p0.01) and in left SA (p0.001). The mean peak velocity (right SPV and left SPV) did not differ significantly between the two groups. When the stimulus is predictable, the saccades in a healthy subject are more timely spaced and accurate than in a patient. When the stimulus is unpredictable, "the memory of the past" has no importance and cannot help in saccade programming, and variability in the healthy subjects increases.

The effect of competing non-target stimuli (distractors) presented together with a target for saccades was investigated with special emphasis on saccadic reaction time. Using the gap task (fixation point offset preceding target onset by 200 msec) high numbers of express saccades were obtained from four human subjects. A single non-target stimulus in the visual hemifield contralateral to the target reduced the number of express saccades. The extend of reduction increased with increasing stimulus size leading to a situation where express saccades were replaced entirely with saccades having a latency mode 30 msec later. Non-target stimuli occurring in the hemifield ipsilateral to the saccade target could also reduce the number of express saccades in favour of fast regular saccades. The effect of ipsilateral non-target stimuli depended mainly on their position in the visual field: ipsilateral non-target stimuli outside the dead zone for express saccades caused only a slight reduction of express saccades. Non-target stimuli invading the dead zone, however, suppressed express saccades almost completely, even though the saccade target appeared well outside the dead zone. The onset of a whole field of bars of one orientation (serving as distractors) simultaneously with the target (consisting of a single bar of another orientation = pop-out condition), suppressed express saccades completely. The same result, however, was obtained with only two distractor bars presented ipsilateral and contralateral within the dead zone for express saccades. Express saccades were present, however, when the whole field of distracting bars was continuously visible throughout the whole trial.

The effect of unilateral circumscribed lesions in different areas of the frontal and parietal cortex on the distribution of saccadic reaction times (SRT) is investigated in 32 neurological patients and 17 normal controls. Among frontal patients only those with a lesion in the FEF region showed an increased percentage of express saccades, especially with saccades towards the side ipsilateral to the lesion. This applied to conditions in which fixation was interrupted prior to target appearance (‘gap paradigm’). With fixation point ‘overlap’ express saccades were largely suppressed, as in normals. All patients with a frontal lesion showed a decreased percentage of contralateral anticipatory saccades. In contrast, the percentages of direction and time errors of these patients were in the normal range. Patients with dorsolateral parietal lesions showed decomposed SRT patterns (high SRT variability, increased percentages of time and direction errors, decreased percentages of express and anticipatory saccades). The decomposition had a contralateral preponderance and increased if more than one stimulus was visible beside the saccade target. The findings are compatible with the notion that the frontal cortex is involved in the voluntary control of visually triggered saccades, and that the parietal cortex mainly deals with visual target selection.

Gaze control was compared between children demonstrating high vs low motor proficiency on the Bruininks-Oseretsky Test of Motor Proficiency. Gaze during the response speed task, which measures reaction to a moving visual stimulus, was observed. Eye events were coded just prior, during, and after the release of the stick in the response speed task. A set of six gazes across seven trials of the task was recorded for all subjects. Low proficiency children were slower to respond to the falling stick than the high proficiency group. High performers tended to use a higher percentage of fixations across all trials. Most noticeble were differences between the groups at the moment of release. For high performers, fixations tended to be much longer, indicating the use of a steady gaze through to the final clamping motion of the thumb on the stick. Additionally, the location of gaze at the moment of release differed noticeably. High performers sustained their gaze on the stick while the low performers were as likely to focus on the stick, off the stick or at their own thumb. This study describes the role of gaze in the performance of tasks requiring a quick response to visual stimuli. The results suggest that differences between between proficient and clumsy motor responses in children may be associated with gaze control.

Saccadic reaction times and amplitudes were determined in four human subjects and two rhesus monkeys when they made saccades to visual targets appearing in different spatial or temporal contexts. Two stimuli were presented at different positions, either simultaneously (global condition) or in random order (range condition). Both the gap and the overlap paradigm were used. The characteristics of different groups of saccades defined by the separate peaks in the distribution of the saccadic reaction times as express and regular saccades, were analysed and compared. It is shown that, in man and monkey, the amplitudes of express saccades undergo the same or even stronger context-dependent changes as do those of regular saccades. Furthermore, the presence or absence of the fixation point also influences the saccadic amplitudes, at least for the express saccades. We conclude that the neural mechanisms that determine the amplitudes of the express saccades are more strictly under the control of the physical and physiological conditions of the stimulus situation, whereas regular saccades have greater — although not complete — dependence on the psychological context and, in particular, the subject's effort.

Saccadic reaction time (SRT), is a good index of visual attention pattern. “Gap/overlap paradigm” is supporting the idea that state of attention (engaged/disengaged) influences the SRT toward stimulus. In “overlap”, fixation point (FP) and target overlap; while in “gap”, FP extinguished before target onset. 200ms gap is associated with reduced RT compared with the overlap (“gap effect”).Boys aged 7-16, with diagnosis of ADHD, ASD or comorbid ASD+ADHD (FSIQ>70) were tested on antisaccades and prosaccades under gap, overlap, and step conditions.Preliminary result of 15 ADHD, 7 ASD and 8 co-morbid subjects is reported with data collection still ongoing. For latency, there was an effect of Task (P< 0.05), i.e. slower latency during antisaccades than prosaccades, and there was an effect of condition (P< 0.05) suggesting increase in latency from gap to step to overlap. These effects were highly significant but independent of group (p=0.7). For error rate there was an effect of task ((P< 0.05; more directional errors in antisaccade than prosaccade) but no effect of condition. Task effect was independent of group, but there was a strong trend towards an effect of Group (p=0.055); this effect indicates that the comorbid group had the lowest error rates compared to the other two groups, who in turn were very similar to each other.These data replicate previously demonstrated saccadic task in patients with ADHD, and ASD. Comparison of the data with a control group will enable us to explain the different patterns of attentional processing in these clinical groups.

We used reversible cold lesions to explore the oculomotor consequences of separate and combined dysfunction of the superior colliculus (SC) and the frontal eye field (FEF). Two monkeys were trained to fixate visual targets. In one we measured visually driven saccades while cooling the right SC, first alone, then in combination with bilateral FEF ablation. Two cryodes in the other subject permitted measurement of eye movements during cooling of either the right FEF or the right SC, or both structures together. Cooling FEF mainly caused a neglect. Raising the cryode temperature slightly alleviated the neglect and uncovered a subtle saccadic deficit. It consisted of a slight reduction in saccadic amplitude and increase in saccadic reaction time. Cooling the SC alone lengthened saccadic reaction time and reduced saccadic amplitude more dramatically, causing the monkeys' initial saccade to miss the target. Some correction occurred but a targeting error persisted to the end of the trial. Combined lesions of FEF and SC greatly increased reaction times, reduced saccadic amplitude, and caused large and persistent targeting errors. The changes in saccadic amplitude and the targeting errors were a function of the monkey's eye position. Combined lesions also truncated the ocular range of the monkeys.

The mean saccadic reaction time (SRT) of a group of dyslexic children was compared to the SRT of a group of normal children and to another group of normal adults. The mean SRT of the dyslexic group was significantly longer than that of the other two groups. The saccades of the dyslexic group had a shorter SRT when they were directed towards the right than when they were directed towards the left. For the other two groups the converse was true. There were no qualitative or quantitative differences between the optokinetically-evoked nystagmus of dyslexic children and that of normal adults.

Control of visual fixations was studied as three stump-tailed macaques (Macaca arctoides) performed on a search task. The presentation of each visual stimulus was delayed for a short time (0-163 msec) after the beginning of a fixation on the location of that stimulus. The duration of visual fixations increased as a function of stimulus onset delay up to 130 msec. However, the increase in fixation duration was only half the stimulus onset delay imposed. This result suggests that oculomotor reactions are facilitated by longer foreperiods in a manner similar to other disjunctive reactions.

Three variables that might influence oculomotor and finger movement reaction times to visual stimuli were combined factorially: the response used to produce each stimulus, the response used to report the target stimulus, and the delay between the stimulus-producing response and the stimulus onset. Stimulus onset delay and the type of stimulus-producing response affected reaction time significantly, but the response used to report the stimulus did not. The stimulus onset delay affected both manual and oculomotor reaction times in a manner similar to that of the warning stimulus in conventional reaction time experiments. Thus, the greater facilitation of oculomotor latency that has been observed in previous visual search experiments cannot be attributed to reaction time warning-stimulus effects.

Saslow (1967) and Fischer and Ramsperger (1984) found that saccadic reaction time (SRT) depends on the interval between the fixation point offset and the target onset. Using a continuously visible fixation point, we asked whether a similar function would be obtained if subjects attended to a peripherally viewed point extinguished at variable intervals before or after the target onset. The interval was varied between -500 ms (i.e., attention stimulus offset after saccade target onset = overlap trials) and 500 ms (i.e., attention stimulus offset before saccade target onset = gap trials). The results show a constant mean SRT of about 240 ms for overlap trials, and a U-shaped function with a minimum of 140 ms, at a gap duration of 200 ms, for gap trials. These findings suggest that saccadic latencies do not depend on the cessation of fixation per se, but rather on the disengagement of attention from any location in the visual field. The time required for subjects to disengage their attention is approximately 100 ms. This disengaged state of attention--during which short latency (express) saccades can be made--can be sustained only for a gap duration of 300 ms. At longer gap durations mean SRTs increase again.

Human subjects were asked to execute a saccade from a central fixation point to a peripheral target at the time of its onset. When the fixation point is turned off some time (approximately equal to 200 ms) before target onset, such that there is a gap where subjects see nothing, the distribution of their saccadic reaction times is bimodal with one narrow peak around 100 ms (express saccades) and another peak around 150 ms (regular saccades) measured from the onset of the target. Express saccades have been described earlier for the monkey.

Monkeys were trained to change their direction of gaze from one point (fixation point) to another (target). If the fixation point was extinguished at the same time when the new target occurred the saccadic reaction times (SRT) were in the order of 200 ms. If the fixation point disappeared 150–250 ms before the new target occurred (gap with no visible stimulus) monkeys made regular saccades after shorter reaction times of about 140 ms. In addition animals in the gap situation made saccades that had reaction times of no more than 70–80 ms measured from the onset of the new target (Express-Saccades). The reaction times of the E-saccades have standard deviations of only ± 3 ms. E-saccades occurred with a frequency of up to 80% for gaps of 200–240 ms. If the gap was shorter than 180 ms increasingly more regular saccades were made with reaction times of 140–160 ms. With gap duration decreasing from 140 ms to zero all saccades were regular with SRTs increasing linearly to more than 200 ms. In one animal almost all E-saccades fell short and were corrected after less than 250 ms depending on the size of the error: large error were corrected faster than small ones.

Recent research indicates that attentional stimulus selection could be a rhythmic process. In monkey, neurons in V4 and IT exhibit rhythmic spiking activity in the theta range in response to a stimulus. When two stimuli are presented together, the rhythmic neuronal responses to each occur in anti-phase, a result indicative of competitive interactions. In addition, it was recently demonstrated that these alternating oscillations in monkey V4 modulate the speed of saccadic responses to a target flashed on one of the two competing stimuli. Here, we replicate a similar behavioral task in humans (7 participants, each performed 4000 trials) and report a pattern of results consistent with the monkey findings: saccadic response times fluctuate in the theta range (6 Hz), with opposite phase for targets flashed on distinct competing stimuli.

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