Characteristics of saccadic eye movements in attentionally handicapped patients.

Some characteristics of saccadic eye movements were investigated electro-oculographically in hemiplegic attentionally handicapped patients and normal subjects under stationary and moving target situations. The velocity of saccadic eye movements was greater and the duration shorter in hemiplegic than in normal subjects. Greater variability of angular velocity and amplitude functions, and of duration and amplitude functions was found among hemiplegic subjects than among normal. The results were explained, in part, by possible differences in the strength of extra-ocular muscle contraction, variables associated with inhibitory control and learning variables.     

Long-lasting modifications of saccadic eye movements following adaptation induced in the double-step target paradigm

The adaptation of saccadic eye movements to environmental changes occurring throughout life is a good model of motor learning and motor memory. Numerous studies have analyzed the behavioral properties and neural substrate of oculomotor learning in short-term saccadic adaptation protocols, but to our knowledge, none have tested the persistence of the oculomotor memory. In the present study, the double-step target protocol was used in five human subjects to adaptively decrease the amplitude of reactive saccades triggered by a horizontally-stepping visual target. We tested the amplitude of visually guided saccades just before and at different times (up to 19 days) after the adaptation session. The results revealed that immediately after the adaptation session, saccade amplitude was significantly reduced by 22% on average. Although progressively recovering over days, this change in saccade gain was still statistically significant on days 1 and 5, with an average retention rate of 36% and 19%, respectively. On day 11, saccade amplitude no longer differed from the pre-adaptation value. Adaptation was more effective and more resistant to recovery for leftward saccades than for rightward ones. Lastly, modifications of saccade gain related to adaptation were accompanied by a decrease of both saccade duration and peak velocity. A control experiment indicated that all these findings were specifically related to the adaptation protocol, and further revealed that no change in the main sequence relationships could be specifically related to adaptation. We conclude that in humans, the modifications of saccade amplitude that quickly develop during a double-step target adaptation protocol can remain in memory for a much longer period of time, reflecting enduring plastic changes in the brain.     

Planning of saccadic eye movements

Most theories of the programming of saccadic eye movements (SEM) agree that direction and amplitude are the two basic dimensions that are under control when an intended movement is planned. But they disagree over whether these two basic parameters are specified separately or in conjunction. We measured saccadic reaction time (SRT) in a situation where information about amplitude and direction of the required movement became available at different moments in time. The delivery of information about either direction or amplitude prior to another reduced duration of SRT demonstrated that direction and amplitude were specified separately rather than in conjunction or in a fixed serial order. All changes in SRT were quantitatively explained by a simple growth-process (accumulator) model according to which a movement starts when two separate neural activities, embodying the direction and amplitude programming, have both reached a constant threshold level of activity. Although, in isolation, the amplitude programming was faster than the direction programming, the situation reversed when two dimensions had to be specified at the same time. We conclude that beside the motor maps representing the desired final position of the eye or a fixed movement vector, another processing stage is required in which the basic parameters of SEM, direction and amplitude, are clearly separable.     

Comparison of effects of small lesions in posterodorsal septum on spontaneous and rerun correction (contingently reinforced) alternation in rats.

In the first part of the experiment, characteristics of T-maze alternation behavior were compared by giving one group of 11 rats seven sessions under conditions of "rerun correction" (contingent reinforcement for alternation) and another group of 11 rats the same number of sessions with noncontingent reinforcements, i.e., entering either goal arm of the T-maze was reinforced. Both groups alternated significantly above chance, and the difference in medians between groups was small but significant in later sessions. However, rats given rerun correction training quickly came against the "ceiling" of 100% alternation, and individual differences were small. The scores of rats run under conditions of "spontaneous" alternation were more variable, both within and between rats. In the second part of the experiment, six rats in each group received small electrolytic lesions in the posterodorsal septum. There were five operated-control rats from each group. After 2-wk postoperative recovery all rats were again given seven sessions in the T-maze. Under rerun correction procedure (contingent reinforcement), the controls retained near-perfect alternation scores. Most animals with lesions dropped to chance levels but recovered to control level over the seven sessions. Rats tested under spontaneous alternation conditions behaved quite differently. The control group continued to alternate significantly, but rats with lesions significantly alternated less and did not recover.     

Haptic detection of sine-wave gratings

We studied human haptic perception of sine-wave gratings. In the first experiment we measured the dependence of amplitude detection thresholds on the number of cycles and on the wavelength of the gratings. In haptic perception of sine-wave gratings, the results are in agreement with neural summation. The rate at which detection thresholds decrease with increasing number of cycles is much higher than can be accounted for by probability summation alone. Further, neural summation mechanisms describe the detection thresholds accurately over the whole spatial range probed in the experiment, that is wavelengths from 14 mm up to 225 mm. Earlier, we found a power-law dependence of thresholds on the spatial width of Gaussian profiles (Louw et al, 2000 Experimental Brain Research 132 369-374). The current results extend these findings; the power-law dependence holds not only for Gaussian profiles, but also for a broad range of sine-wave gratings with the number of cycles varying between 1 and 8. Haptic perception involves tactual scanning combined with an active, dynamic exploration of the environment. We measured characteristics of the velocity and force with which stimuli were scanned while performing a psychophysical task. One particularly surprising finding was that, without being instructed, participants maintained an almost constant scanning velocity during each 45-min session. A constant velocity in successive trials of the experiment might facilitate or even be necessary for discrimination. Further, a large systematic dependence of velocity on scanning length was found. An eightfold increase in scanning length resulted in about a fourfold increase in scanning velocity. A second experiment was conducted to study the influence of scanning velocity on psychophysical detection thresholds. This was done by systematically imposing specific scanning velocities to the participants while the thresholds were measured. The main result of the second experiment was that psychophysical detection thresholds are constant over a relatively broad range of scanning velocities.     

The Role of Emotional Content and Perceptual Saliency During the Programming of Saccades Toward Faces

Previous studies have shown that the human visual system can detect a face and elicit a saccadic eye movement toward it very efficiently compared to other categories of visual stimuli. In the first experiment, we tested the influence of facial expressions on fast face detection using a saccadic choice task. Face-vehicle pairs were simultaneously presented and participants were asked to saccade toward the target (the face or the vehicle). We observed that saccades toward faces were initiated faster, and more often in the correct direction, than saccades toward vehicles, regardless of the facial expressions (happy, fearful, or neutral). We also observed that saccade endpoints on face images were lower when the face was happy and higher when it was neutral. In the second experiment, we explicitly tested the detection of facial expressions. We used a saccadic choice task with emotional-neutral pairs of faces and participants were asked to saccade toward the emotional (happy or fearful) or the neutral face. Participants were faster when they were asked to saccade toward the emotional face. They also made fewer errors, especially when the emotional face was happy. Using computational modeling, we showed that this happy face advantage can, at least partly, be explained by perceptual factors. Also, saccade endpoints were lower when the target was happy than when it was fearful. Overall, we suggest that there is no automatic prioritization of emotional faces, at least for saccades with short latencies, but that salient local face features can automatically attract attention.     

Differentiating between verbal and spatial encoding using eye-movement recordings

Visual information processing is guided by an active mechanism generating saccadic eye movements to salient stimuli. Here we investigate the specific contribution of saccades to memory encoding of verbal and spatial properties in a serial recall task. In the first experiment, participants moved their eyes freely without specific instruction. We demonstrate the existence of qualitative differences in eye-movement strategies during verbal and spatial memory encoding. While verbal memory encoding was characterized by shifting the gaze to the to-be-encoded stimuli, saccadic activity was suppressed during spatial encoding. In the second experiment, participants were required to suppress saccades by fixating centrally during encoding or to make precise saccades onto the memory items. Active suppression of saccades had no effect on memory performance, but tracking the upcoming stimuli decreased memory performance dramatically in both tasks, indicating a resource bottleneck between display-controlled saccadic control and memory encoding. We conclude that optimized encoding strategies for verbal and spatial features are underlying memory performance in serial recall, but such strategies work on an involuntary level only and do not support memory encoding when they are explicitly required by the task.     

气质与眼动控制的关系

本研究采用眼动追踪和问卷测量相结合的方法,对气质类型和眼动控制的关系进行了探讨。眼动实验为2（眼跳方向：朝向眼跳和反向眼跳）X 2（任务类型：重复眼跳和转换眼跳）组内设计;气质分数用陈会昌编制的《气质类型测试量表》测量。结果表明,气质分数与眼动特性之间存在显著的相关性,不同气质类型（神经活动类型）在抑制过程和任务重置过程中表现出不同的相互作用模式。具体而言,神经活动强度是一个基本维度,它与认知控制的抑制功能和转换功能都有着密切联系;而神经活动的灵活性和平衡性则分别是转换功能和抑制功能的重要条件。     

Speed-Accuracy Characteristics of Saccadic Eye Movements

Speed-accuracy trade-off characteristic of horizontal saccadic eye movements were examined in this study. Unlike limb movements, saccadic eye movements are preprogrammed, unidimensional, and do not involve target impact. Hence, they provide an optimal test of the impulse variability account of the speed-accuracy trade-off in rapid movements. Subjects were required to alternately look at two target lights as fast and as accurately as possible for a period of 10 s. Target lights subtended angles of 5,10,15, and 20°. By restricting target distances to less than 20° of arc, the speed-accuracy relation was examined for single horizontal saccadic movements of the eye. Movement of the dominant eye was tracked with an infra-red eye monitoring device. Fifty saccadic movements of the eye were recorded for each target distance and used to compute the average amplitude, duration, and velocity of eye movements, as well as, movement endpoint variability. An increase in both average velocity and movement endpoint variability with increasing movement amplitude was found. This, together with the unique features of the eye movement system, support the impulse variability account of the speed-accuracy trade-off in rapid movements.     

Speed-accuracy characteristics of saccadic eye movements

Speed-accuracy trade-off characteristic of horizontal saccadic eye movements were examined in this study. Unlike limb movements, saccadic eye movements are preprogrammed, unidimensional, and do not involve target impact. Hence, they provide an optimal test of the impulse variability account of the speed-accuracy trade-off in rapid movements. Subjects were required to alternately look at two target lights as fast and as accurately as possible for a period of 10 s. Target lights subtended angles of 5, 10, 15, and 20 degrees. By restricting target distances to less than 20 degrees of arc, the speed-accuracy relation was examined for single horizontal saccadic movements of the eye. movement of the dominant eye was tracked with an infra-red eye monitoring device. Fifty saccadic movements of the eye were recorded for each target distance and used to compute the average amplitude, duration, and velocity of eye movements, as well as, movement endpoint variability. An increase in both average velocity and movement endpoint variability with increasing movement amplitude was found. This, together with the unique features of the eye movement system, support the impulse variability account of the speed-accuracy trade-off in rapid movements.     

Religious Context and Prosociality: An Experimental Study from Valparaíso,Chile

Are people more prosocial in a religious context? We addressed this question through an experiment. We randomly placed participants in the control group in a neutral location (a lecture hall), and we placed participants in the experimental group in a religious location (a chapel). The participants then took part in a one‐shot three‐person public goods game, which measured participants’ degree of cooperativeness. The results showed that participants in the experimental group cooperated significantly more than did participants in the control group. Furthermore, participants’ beliefs about other participants’ cooperativeness were more positive in the experimental group than they were in the control group. Improved expectations of others partially explained the enhanced cooperation in the religious context. We found no main or interaction effect of self‐reported religiosity in the experiment.     

Reduced misinformation effects following saccadic bilateral eye movements

The effects of saccadic bilateral (horizontal) eye movements on memory for a visual event narrative were investigated. In the study phase, participants were exposed to a set of pictures accompanied by a verbal commentary describing the events depicted in the pictures. Next, the participants were asked either misleading or control questions about the depicted event and were then asked to engage in 30s of bilateral vs. vertical vs. no eye movements. Finally, recognition memory was tested using the remember-know procedure. It was found that bilateral eye movements increased true memory for the event, increased recollection, and decreased the magnitude of the misinformation effect. The findings are discussed in terms of source monitoring, dual-process theories of memory and the potential neural foundations of such effects.     

Practice variability promotes an external focus of attention and enhances motor skill learning

Variability in practice has been shown to enhance motor skill learning. Benefits of practice variability have been attributed to motor schema formation (variable versus constant practice), or more effortful information processing (random versus blocked practice). We hypothesized that, among other mechanisms, greater practice variability might promote an external focus of attention on the intended movement effect, while less variability would be more conducive to a less effective internal focus on body movements. In Experiment 1, the learning of a throwing task was enhanced by variable versus constant practice, and variable group participants reported focusing more on the distance to the target (external focus), while constant group participants focused more on their posture (internal focus). In Experiment 2, golf putting was learned more effectively with a random compared with a blocked practice schedule. Furthermore, random group learners reported using a more effective distal external focus (i.e., distance to the target) to a greater extent, whereas blocked group participants used a less effective proximal focus (i.e., putter) more often. While attentional focus was assessed through questionnaires in the first two experiments, learners in Experiment 3 were asked to report their current attentional focus at any time during practice. Again, the learning of a throwing task was more effective after random relative to blocked practice. Also, random practice learners reported using more external focus cues, while in blocked practice participants used more internal focus cues. The findings suggest that the attentional foci induced by different practice schedules might be at least partially responsible for the learning differences.     

Reinforcing variability in adolescents with autism

Five adolescents with autism, 5 adult control participants, and 4 child controls received rewards for varying their sequences of responses while playing a computer game. In preceding and following phases, rewards were provided at approximately the same rate but were independent of variability. The most important finding was that, when reinforced, variability increased significantly in all groups. Reinforced variability could provide the necessary behavioral substrate for individuals with autism to learn new responses.     

Interdependence of Saccadic and Fixational Fluctuations

Recent research suggests that the different components of eye movements (fixations, saccades) are not strictly separate but are interdependent processes. This argument rests on observations that gaze-step sizes yield unimodal distributions and exhibit power-law scaling, indicative of interdependent processes coordinated across timescales. The studies that produced these findings, however, employed complex tasks (visual search, scene perception). Thus, the question is whether the observed interdependence is a fundamental property of eye movements or emerges in the interplay between cognitive processes and complex visual stimuli. In this study, we used a simple eye movement task where participants moved their eyes in a prescribed sequence at several different paces. We outlined diverging predictions for this task for independence versus interdependence of fixational and saccadic fluctuations and tested these predictions by assessing the spectral properties of eye movements. We found no clear peak in the power spectrum attributable exclusively to saccadic fluctuations. Furthermore, changing the pace of the eye movement sequence yielded a global shift in scaling relations evident in the power spectrum, not just a localized shift for saccadic fluctuations. These results support the conclusion that fixations and saccades are interdependent processes.     

The reinforcement of least-frequent interresponse times

A new schedule of reinforcement was used to maintain key-pecking by pigeons. The schedule reinforced only pecks terminating interresponse times which occurred least often relative to the exponential distribution of interresponse times to be expected from an ideal random generator. Two schedule parameters were varied: (1) the rate constant of the controlling exponential distribution and (2) the probability that a response would be reinforced, given that it met the interresponse-time contingency. Response rate changed quickly and markedly with changes in the rate constant; it changed only slightly with a fourfold change in the reinforcement probability. The schedule produced stable rates and high intra- and inter-subject reliability, yet interresponse time distributions were approximately exponential. Such local interresponse time variability in the context of good overall control suggests that the schedule may be used to generate stable, predictable, yet sensitive baseline rates. Implications for the measurement of rate are discussed.     

Paced and self-paced continuous reaction time

Studies of the effect of pacing in continuous RT tasks are inconclusive. They have failed to (1) compare paced and self-paced RT at matched error rates and (2) examine RT distributions as well as mean or median RT. In the present experiment RTs were corrected for error rate by relating them to the speed-accuracy tradeoff function, which was measured in each experimental session. In this way deciles of the RT distributions of paced and self-paced conditions were compared, for eight subjects and four successive sessions. The task was a four-choice continuous RT task, employing visual stimuli. The results show that RT distributions are wider in the paced conditions. RTs of the first deciles are faster for pacing whereas medians in paced and self-paced conditions are about equal. The results can be explained when it is assumed that the variable R-S intervals in paced conditions lead to a larger variability of RT.     

Control of responding by the elements of a compound discriminative stimulus and by the elements as individual discriminative stimuli

In the first of two studies, the responding of four albino rats was differentially reinforced in the presence of noise and light together and then tested in the presence of the noise and the light separately during extinction. The light exercised substantially more control of responding than did the noise. In the second study the responding of a similar group of four rats was differentially reinforced in the presence of the noise and the light separately. Control of responding by the light developed more rapidly than control by the noise. Results suggest that levels of control by stimuli after differential reinforcement with respect to the stimuli together can be predicted by the rates of development of control during differential reinforcement with respect to the stimuli separately.     

Neural and behavioral effects of interference resolution in depression and rumination

Individuals diagnosed with major depressive disorder (MDD) often ruminate about their depression and their life situations, impairing their concentration and performance on daily tasks. We examined whether rumination might be due to a deficit in the ability to expel negative information from short-term memory (STM), and fMRI was used to examine the neural structures involved in this ability. MDD and healthy control (HC) participants were tested using a directed-forgetting procedure in a short-term item recognition task. As predicted, MDD participants had more difficulty than did HCs in expelling negative, but not positive, words from STM. Overall, the neural networks involved in directed forgetting were similar for both groups, but the MDDs exhibited more spatial variability in activation in the left inferior frontal gyrus (a region critical for inhibiting irrelevant information), which may contribute to their relative inability to inhibit negative information.     

Adaptation of Reactive Saccades is Influenced by Unconscious Priming of the Attention Focus

The authors investigated whether the size of the attention focus can influence saccadic adaptation, and whether this influence changes in older age. Using the scrambled sentence task, young and older participants were either primed for a wide attention focus, or primed of a narrow attention focus, or were not primed for any specific attention focus. Subsequently, all participants underwent a double-step saccadic adaptation paradigm aimed at changing the direction of reflexive saccades. The authors found that compared to the nonprimed control group, priming for a wide attention focus enhanced saccadic adaptation in both age groups by a similar amount; the benefit persisted throughout the adaptation phase, but was absent during the deadaptation phase. In contrast, the authors found no effects of priming with a narrow attention focus on saccadic adaptation. From this the authors conclude that a wide attention focus is beneficial for workaround strategies but not for adaptive recalibration, and that those benefits are similar in young and older persons.