Fixation disengagement and eye-movement latency

We examined eye-movement latencies to a target that appeared during visual fixation of a stationary stimulus, a moving stimulus, or an extrafoveal stimulus. The stimulus at fixation was turned off either before target onset (gap condition) or after target onset (overlap condition). Consistent with previous research, saccadic latencies were shorter in gap conditions than they were in overlap conditions (the gap effect). In Experiment 1, a gap effect was observed for vergence eye movements. In Experiment 2, a gap effect was observed for saccades directed at a target that appeared during visual pursuit of a moving stimulus. In Experiment 3, a gap effect was observed for saccades directed at a target that appeared during extrafoveal fixation. The present results extend reports of the gap effect for saccadic shifts during visual fixation to (a) vergence shifts during visual fixation, (b) saccadic shifts during smooth visual pursuit, and (c) saccadic shifts during extrafoveal fixation. The present findings are discussed with respect to the incompatible goals of fixation-locking and fixation-shifting oculomotor responses.     

Effects of direct and averted gaze on the subsequent saccadic response

The saccadic latency to visual targets is susceptible to the properties of the currently fixated objects. For example, the disappearance of a fixation stimulus prior to presentation of a peripheral target shortens saccadic latencies (the gap effect). In the present study, we investigated the influences of a social signal from a facial fixation stimulus (i.e., gaze direction) on subsequent saccadic responses in the gap paradigm. In Experiment 1, a cartoon face with a direct or averted gaze was used as a fixation stimulus. The pupils of the face were unchanged (overlap), disappeared (gap), or were translated vertically to make or break eye contact (gaze shift). Participants were required to make a saccade toward a target to the left or the right of the fixation stimulus as quickly as possible. The results showed that the gaze direction influenced saccadic latencies only in the gaze shift condition, but not in the gap or overlap condition; the direct-to-averted gaze shift (i.e., breaking eye contact) yielded shorter saccadic latencies than did the averted-to-direct gaze shift (i.e., making eye contact). Further experiments revealed that this effect was eye contact specific (Exp. 2) and that the appearance of an eye gaze immediately before the saccade initiation also influenced the saccadic latency, depending on the gaze direction (Exp. 3). These results suggest that the latency of target-elicited saccades can be modulated not only by physical changes of the fixation stimulus, as has been seen in the conventional gap effect, but also by a social signal from the attended fixation stimulus.     

Effects of perceptual quality on the processing of human faces presented to the left and right cerebral hemispheres

Three experiments examined the effects of stimulus duration, retinal eccentricity, and visual noise on the processing of human faces presented to the left visual field/right hemisphere (LVF-RH) and right visual field/left hemisphere (RVF-LH). In Experiment 1 observers identified which of 10 similar male faces was presented on a screen. The single face was presented for 10, 55, or 100 ms at 1 degree, 4 degrees, or 9 degrees of visual angle to the left or right of fixation. Decreasing stimulus duration and increasing retinal eccentricity lowered face recognition. The effect of duration was the same for LVF-RH and RVF-LH trials, but the detrimental effect of increasing retinal eccentricity was larger on LVF-RH trials than on RVF-LH trials. In Experiment 2 observers indicated whether a single face from this same set was a member of a memorized set of five positive faces. The probe face on each trial was presented alone or embedded in visual noise. Visual noise increased the error rate more on LVF-RH trials than on RVF-LH trials. This effect was replicated in Experiment 3, which also required observers to make a much easier discrimination between male and female faces. In the male/female task visual noise tended to impair performance more on RVF-LH trials than on LVF-RH trials, opposite the effect for the male/male task. These results are discussed in terms of hemispheric asymmetry for global versus local features of faces, the level of feature analysis demanded by a task, and the level of feature analysis most disrupted by perceptual degradation.     

What are human express saccades?

When a fixation point is removed 200 msec prior to target onset (the gap condition), human subjects are said to produce eye movements that have a short latency (80–120 msec), that form the early peak of a bimodal latency distribution, and that have been labeled “human express saccades” (see, e.g., Fischer, 1987; Fischer & Breitmeyer, 1987; Fischer & Ramsperger, 1984, 1986). In three experiments, we sought to obtain this express saccade diagnostic pattern in the gap condition, We orthogonally combined target location predictability with the presence versus absence of catch trials (Experiment 1). When target location was fixed and catch trials were not used, we found mostly anticipations. In the remaining conditions, where responses were under stimulus control, bimodality was not frequently observed, and, whether it was or not, latencies were not in the express saccade range. Using random target locations, we then varied stimulus luminance and the mode of stimulus presentation (LEDs vs. oscilloscope) in the gap and overlap (fixation is not removed) conditions (Experiment2). Bimodality was rarely observed, the gap effect (overlap minus gap reaction time) was additive with luminance, and only the brightest targets elicited saccades in the express range. When fixed locations and no catch trials were combined with latency feedback (Experiment 3), we observed many responses in the express saccade range and some evidence for bimodality, but the sudden introduction of catch trials revealed that many early responses were not under stimulus control. Humanscan make stimulus-controlled saccades that are initiated very rapidly (80–120 msec), but unless catch trials or choice reaction time is used, it is not possible to distinguish such saccades from anticipatory responses that are prepared in advance and timed to occur shortly after target onset. Because the express saccade diagnostic pattern is not a characteristic feature of human saccadic performance, we urge investigators to focus their attention on the robustgap effect     

A central-peripheral asymmetry in masked priming

Masked primes presented prior to a target result in behavioral benefits on incompatible trials (in which the prime and the target are mapped onto opposite responses) when they appear at fixation, but in behavioral benefits on compatible trials (in which the prime and the target are mapped onto the same response) when appearing peripherally. In Experiment 1, the time course of this central-peripheral asymmetry (CPA) was investigated. For central primes, compatible-trial benefits at short stimulus onset asynchronies (SOAs) turned into incompatible-trial benefits at longer SOAs. For peripheral primes, compatible-trial benefits at short SOAs increased in size with longer SOAs. Experiment 2 showed that these effects also occur when primes and targets are physically dissimilar, ruling out an interpretation in terms of the perceptual properties of the stimulus material. In Experiments 3 and 4, the question was investigated as to whether the CPA is related to visual-spatial attention and/or retinal eccentricity per se. The results indicate that the CPA is independent of attentional factors but strongly related to the physiological inhomogeneity of the retina. It is argued that central and peripheral primes trigger an initial motor activation, which is inhibited only if primes are presented at retinal locations of sufficiently high perceptual sensitivity. The results are discussed in terms of an activation threshold model.     

视网膜离心率影响空间注意梯度分布

采用同步判断(Simultaneous judgment, SJ)的研究范式探讨空间注意梯度是否受到视网膜离心率的影响。实验中给被试呈现两个目标刺激, 调节它们的呈现距离和间隔时间, 让被试进行不限时的同步判断, 计算出各种距离上的主观等同点(Point of Subjective Simultaneous, PSS)变化情况。实验中对比了注视点和注意点重合与分离的两种状态。其中注视点和注意点分离的状态是指使用反向掩蔽后的线索刺激将注意点内隐地引导到外周。通过控制似动等影响因素, 发现在注意点和注视点分离的状态下存在距离效应—— 也就是随着距离的增长主观等同点变化越大, 但是在重合的状态下则没有。结果表明分离状态下存在传统意义上的注意梯度效应, 而重合时, 注意易化梯度受到一个抑制梯度的影响。这说明, 注意梯度分布受到视网膜离心率的影响, 而影响方式符合注意点为中心的易化梯度场和注视点为中心的抑制梯度场的双梯度场理论。     

Motion and position shifts induced by the double-drift stimulus are unaffected by attentional load

The double-drift stimulus produces a strong shift in apparent motion direction that generates large errors of perceived position. In this study, we tested the effect of attentional load on the perceptual estimates of motion direction and position for double-drift stimuli. In each trial, four objects appeared, one in each quadrant of a large screen, and they moved upward or downward on an angled trajectory. The target object whose direction or position was to be judged was either cued with a small arrow prior to object motion (low attentional load condition) or cued after the objects stopped moving and disappeared (high attentional load condition). In Experiment 1, these objects appeared 10° from the central fixation, and participants reported the perceived direction of the target’s trajectory after the stimulus disappeared by adjusting the direction of an arrow at the center of the response screen. In Experiment 2, the four double-drift objects could appear between 6 ° and 14° from the central fixation, and participants reported the location of the target object after its disappearance by moving the position of a small circle on the response screen. The errors in direction and position judgments showed little effect of the attentional manipulation—similar errors were seen in both experiments whether or not the participant knew which double-drift object would be tested. This suggests that orienting endogenous attention (i.e., by only attending to one object in the precued trials) does not interact with the strength of the motion or position shifts for the double-drift stimulus.     

Why are there eccentricity effects in visual search? Visual and attentional hypotheses

In standard visual search experiments, observers search for a target item among distracting items. The locations of target items are generally random within the display and ignored as a factor in data analysis. Previous work has shown that targets presented near fixation are, in fact, found more efficiently than are targets presented at more peripheral locations. This paper proposes that the primary cause of this “eccentricity effect” (Carrasco, Evert, Chang, & Katz, 1995) is an attentional bias that allocates attention preferentially to central items. The first four experiments dealt with the possibility that visual, and not attentional, factors underlie the eccentricity effect. They showed that the eccentricity effect cannot be accounted for by the peripheral reduction in visual sensitivity, peripheral crowding, or cortical magnification. Experiment 5 tested the attention allocation model and also showed that RT X set size effects can be independent of eccentricity effects. Experiment 6 showed that the effective set size in a search task depends, in part, on the eccentricity of the target because observers search from fixation outward.     

Deployment of attention to the configuration of features in facelike patterns by ten-week-old infants

Abstract

Three experiments were conducted to investigate the response of 10-week-old infants to the configuration of features in facelike patterns. In each experiment a series of preview trials was shown before. facelike patterns were presented on test trials. Preview stimuli were schematic drawings with non-facial configurations (Experiment 1), schematic drawings with facial configurations (Experiment 2), or photographs of men's and women's faces (Experiment 3). Test stimuli in all three experiments were facelike drawings that differed in the number and the configuration of their stimulus features.     

Simon-type effects: chronometric evidence for keypress schemata in typewriting

In 4 experiments, chronometric evidence for keypress schemata in typing was sought by presenting stimuli to be typed in positions that were displaced from a central fixation point. Reaction times were shorter when stimulus positions corresponded to keyboard locations of the letters to be typed, suggesting that position was an important part of the internal representation of the response. Experiment 1 presented single letters left and right of fixation. Experiment 2 presented single letters above and below fixation. Experiment 3 presented words left and right of fixation and found evidence of parallel activation of keypress schemata. Experiment 4 found no effect of the eccentricity of the keyboard locations and responding fingers, suggesting that response-location codes are categorical, not metric. The results are consistent with D. E. Rumelhart and D. A. Norman's (1982) theory of typewriting.     

Control of reflexive and voluntary saccades in the gap effect

In two experiments, we examined whether voluntary and reflexive saccades shared a common fixation disengagement mechanism, Participants were required to perform a variety of tasks, each requiring a different level of information processing of the display prior to execution of the saccade. In Experiment 1, participants executed either a prosaccade or an antisaccade upon detecting a stimulus array. In Experiment 2, participants executed a prosaccade to a stimulus array only if the array contained a target item. The target could be a line (easy search) or a digit (difficult search). The critical manipulation in both experiments was the relative timing between the removal of the fixation stimulus and the onset of the stimulus array. In both experiments, it was found that saccadic latencies were shortest when the fixation stimulus was removed before the onset of the stimulus array—a gap effect. It was concluded that reflexive and voluntary saccades share a common fixation disengagement mechanism that is largely independent of higher level cognitive processes.     

Control' of reflexive and voluntary saccades in the gap effect.

In two experiments, we examined whether voluntary and reflexive saccades shared a common fixation disengagement mechanism. Participants were required to perform a variety of tasks, each requiring a different level of information processing of the display prior to execution of the saccade. In Experiment 1, participants executed either a prosaccade or an antisaccade upon detecting a stimulus array. In Experiment 2, participants executed a prosaccade to a stimulus array only if the array contained a target item. The target could be a line (easy search) or a digit (difficult search). The critical manipulation in both experiments was the relative timing between the removal of the fixation stimulus and the onset of the stimulus array. In both experiments, it was found that saccadic latencies were shortest when the fixation stimulus was removed before the onset of the stimulus array--a gap effect. It was concluded that reflexive and voluntary saccades share a common fixation disengagement mechanism that is largely independent of higher level cognitive processes.     

The gap effect for eye and hand movements

A temporal gap between fixation point offset and stimulus onset typically yields shorter saccadic latencies to the stimulus than if the fixation stimulus remained on. Several researchers have explored the extent to which this gap also reduces latencies of other responses but have failed to find a gap effect isolated from general warning effects. Experiment 1, however, showed a robust gap effect for aimed hand movements (which required determination of a precise spatial location), regardless of whether the hand moved alone or was accompanied by a saccadic eye movement. Experiment 2 replicated this aimed hand gap effect and also showed a smaller effect for choice manual keypress responses (which required determination of the direction of response only). Experiment 3 showed no gap effect for simple manual keypress responses (which required no spatial determination). The results are consistent with an interpretation of the gap effect in terms of facilitation of spatially oriented responses.     

S-R compatibility effects due to context-dependent spatial stimulus coding

Responses are faster with spatial S-R correspondence than with noncorrespondence (spatial compatibility effect), even if stimulus location is irrelevant (Simon effect). In two experiments, we sought to determine whether stimuli located above and below a fixation point are coded as left and right (and thus affect the selection of left and right responses) if the visual context suggests such a coding. So, stimuli appeared on the left or right eye of a face’s image that was tilted by 90° to one side or the other (Experiment 1) or varied between upright and 45° or 90° tilting (Experiment 2). Whether stimulus location was relevant (Experiment 1) or not (Experiment 2), responses were faster with correspondence of (face-based) stimulus location and (egocentrically defined) response location, even if stimulus and response locations varied on physically orthogonal dimensions. This suggests that object-based spatial stimulus codes are formed automatically and thus influence the speed of response selection.     

Determinants of central processing order in psychological refractory period paradigms: central arrival times, detection times, or preparation?

Three psychological refractory period (PRP) experiments were conducted to assess the effect of central arrival times at the bottleneck on task order scheduling. In Experiment 1, a visual first task (plus-minus symbol discrimination) was combined with an auditory second task (left-right tone judgement) in a standard PRP paradigm with constant task order. In Experiment 2, the order of the tasks varied unpredictably. In Experiment 3, visual-auditory dual-task trials were randomly mixed with single-task trials. To dissociate central arrival times from stimulus detection times, the perceptual stage of the visual task was extended using stimulus degradation. Most importantly, no evidence for a first-come, first-served principle at the central bottleneck was found with the employed paradigms. Instead, the results indicated that preparation (Experiment 1) and the detection times of the stimuli (Experiments 2 and 3) were the main determinants of central processing order in the present study. In the light of previous research, the results indicate that central processing order can be influenced by various factors. The interplay between these factors seems to depend highly on the conditions and requirements of the employed experimental paradigm.     

The role of attention in the facilitation effect and another "inhibition of return"

The present study investigated how anticipation of a target's appearance affects human attention to gaze cues provided by a schematic face. Subjects in a 'catch' group received a high number of 'catch' trials, in which no target stimulus appeared. Subjects in the control group did not receive any catch trials. As in previous studies, both groups showed a facilitation effect to the cued location during shorter stimulus onset asynchrony (SOA). In both groups, an analysis of eye movements confirmed that subjects' eyes remained on the fixation point, ruling out the possibility that the facilitation effect was due to shifting eye movements (saccades) as opposed to a shift in covert attention. But while the control group's response time (RT) decreased as SOA increased, the catch group's RT had a U-shaped pattern and the facilitation effect to the cued location was reversed at the longest SOA (1005 ms). These results suggest that subjects in the catch group disengaged their attention during long SOAs because they expected the trial to be a catch trial. This disengagement of attention during long SOAs results in a delay before attention could be re-focused to the previous location regardless of the cue validity ["IOR (inhibition of return)"-like-phenomenon]. Unlike the conventional IOR, we suggest that this "IOR"-like phenomenon caused by an unpredictive central gaze cue is likely to be mediated by an endogenous mechanism.     

The reduction of saccadic latency by prior offset of the fixation point: an analysis of the gap effect

The latency to initiate a saccade (saccadic reaction time) to an eccentric target is reduced by extinguishing the fixation stimulus prior to the target onset. Various accounts have attributed this latency reduction (referred to as the gap effect) to facilitated sensory processing, oculomotor readiness, or attentional processes. Two experiments were performed to explore the relative contributions of these factors to the gap effect. Experiment 1 demonstrates that the reduction in saccadic reaction time (RT) produced by fixation point offset is additive with the effect of target luminance. Experiment 2 indicates that the gap effect is specific for saccades directed toward a peripheral target and does not influence saccades directed away from the target (i.e., antisaccades) or choice-manual RT. The results are consistent with an interpretation of the gap effect in terms of facilitated premotor processing in the superior colliculus.     

Discrimination learning during the first year: stimulus and positional cues

In four studies, 3-, 6-, and 9-month-old human infants were tested in a discrimination learning task in which visual fixation to a particular stimulus or lateral position was reinforced with an auditory stimulus. In Experiment 1, all age groups exhibited acquisition, extinction, and reinstatement of fixation to the reinforced target or position. Experiment 2 revealed that 3-month-olds retained the positional discrimination but not the stimulus discrimination after a 5-min delay between acquisition and extinction; older infants retained both types of discriminations. In Experiments 3 and 4 we investigated a possible developmental shift in the dominance of positional versus stimulus cues by training infants on displays in which stimulus and position were confounded and then by dissociating the cues on test trials. Results from both experiments indicated positional cue dominance for young infants and stimulus cue dominance for older infants. The findings are discussed in terms of differences in the attentional demands elicited by proprioceptive versus exteroceptive cues.     

Attentional Bias for Threat: Evidence for Delayed Disengagement from Emotional Faces

The present paper reports three new experiments suggesting that the valence of a face cue can influence attentional effects in a cueing paradigm. Moreover, heightened trait anxiety resulted in increased attentional dwell-time on emotional facial stimuli, relative to neutral faces. Experiment 1 presented a cueing task, in which the cue was either an "angry", "happy", or "neutral" facial expression. Targets could appear either in the same location as the face (valid trials) or in a different location to the face (invalid trials). Participants did not show significant variations across the different cue types (angry, happy, neutral) in responding to a target on valid trials. However, the valence of the face did affect response times on invalid trials. Specifically, participants took longer to respond to a target when the face cue was "angry" or "happy" relative to neutral. In Experiment 2, the cue-target stimulus onset asynchrony (SOA) was increased and an overall inhibition of return (IOR) effect was found (i.e., slower responses on valid trials). However, the "angry" face cue eliminated the IOR effect for both high and low trait anxious groups. In Experiment 3, threat-related and jumbled facial stimuli reduced the magnitude of IOR for high, but not for low, trait-anxious participants.These results suggest that: (i) attentional bias in anxiety may reflect a difficulty in disengaging from threat-related and emotional stimuli, and (ii) threat-related and ambiguous cues can influence the magnitude of the IOR effect.     

Holistic face perception: Mind the gap!

The most widely used measurement of holistic face perception, the composite face effect (CFE), is challenged by two apparently contradictory goals: having a defined face part (i.e., the top half), and yet perceiving the face as an integrated unit (i.e., holistically). Here, we investigated the impact of a small gap between top and bottom face halves in the standard composite face paradigm, requiring matching of sequentially presented top face halves. In Experiment 1, the CFE was larger for no-gap than gap stimuli overall, but not for participants who were presented with gap stimuli first, suggesting that the area of the top face half was unknown without a gap. This was confirmed in Experiment 2, in which these two stimulus sets were mixed up: the gap stimuli thus provided information about the area of a top face half and the magnitude of the CFE did not differ between stimulus sets. These observations indicate that the CFE might be artificially inflated in the absence of a stimulus cue that objectively defines a border between the face halves. Finally, in Experiment 3, observers were asked to determine which of two simultaneously presented faces was the composite face. Perceptual judgements for no-gap stimuli approached ceiling; however, with a gap, participants were almost unable to distinguish the composite face from a veridical face. This effect was not only due to low-level segmentation cues at the border of no-gap face halves, because stimulus inversion decreased performance in both conditions. This result indicates that the two halves of different faces may be integrated more naturally with a small gap that eliminates an enhanced contrast border. Collectively, these observations suggest that a small gap between face halves provides an objective definition of the face half to match and is beneficial for valid measurement of the behavioural CFE.