The control of saccade trajectories: direction of curvature depends on prior knowledge of target location and saccade latency

Recent reports have shown that saccades can deviate either toward or away from distractors. However, the specific conditions responsible for the change in initial saccade direction are not known. One possibility, examined here, is that the direction of curvature (toward or away from distractors) reflects preparatory tuning of the oculomotor system when the location of the target and distractor are known in advance. This was investigated by examining saccade trajectories under predictable and unpredictable target conditions. In Experiment 1, the targets and the distractors appeared unpredictably, whereas in Experiment 2 an arrow cue presented at fixation indicated the location of the forthcoming target prior to stimulus onset. Saccades were made to targets on the horizontal, vertical, and principal oblique axis, and distractors appeared simultaneously at an adjacent location (a separation of +/- 45 degrees of visual angle). On average, saccade trajectories curved toward distractors when target locations were unpredictable and curved away from distractors when target locations were known in advance. There was no overall difference in mean saccade latencies between the two experiments. The magnitude of the distractor modulation of saccade trajectory (either toward or away from) was comparable across the different saccade directions (horizontal, vertical, and oblique). These results are interpreted in terms of the time course of competitive interactions operating in the neural structures involved in the suppression of distractors and the selection of a saccade target. A relatively slow mechanism that inhibits movements to distractors produces curvature away from the distractor. This mechanism has more time to operate when target location is predictable, increasing the likelihood that the saccade trajectory will deviate away from the distractor.     

The role of configuration and target discriminability in a visual search task

Ss sorted through decks of cards bearing five-element patterns, separating those in which all five were identical from those in which one of the five was different from the remaining four. Sorting time depended on the configuration and size of the pattern in which the elements were arranged but was independent of the goodness of these patterns. It was concluded that Ss did not attend to the patterns themselves, but just to the elements comprising them in searching for the discrepant element. The differences owing to the patterns appear to be due in part to the compactness of the configurations.     

Probing the attentional control theory in social anxiety: An emotional saccade task

Volitional attentional control has been found to rely on prefrontal neuronal circuits. According to the attentional control theory of anxiety, impairment in the volitional control of attention is a prominent feature in anxiety disorders. The present study investigated this assumption in socially anxious individuals using an emotional saccade task with facial expressions (happy, angry, fearful, sad, neutral). The gaze behavior of participants was recorded during the emotional saccade task, in which participants performed either pro- or antisaccades in response to peripherally presented facial expressions. The results show that socially anxious persons have difficulties in inhibiting themselves to reflexively attend to facial expressions: They made more erratic prosaccades to all facial expressions when an antisaccade was required. Thus, these findings indicate impaired attentional control in social anxiety. Overall, the present study shows a deficit of socially anxious individuals in attentional control—for example, in inhibiting the reflexive orienting to neutral as well as to emotional facial expressions. This result may be due to a dysfunction in the prefrontal areas being involved in attentional control.     

Effects of retinal eccentricity and acuity on global-motion processing

The present study assessed direction discrimination with moving random-dot cinematograms at retinal eccentricities of 0, 8, 22, and 40?deg. In addition, Landolt-C acuity was assessed at these eccentricities to determine whether changes in motion discrimination performance covaried with acuity in the retinal periphery. The results of the experiment indicated that discrimination thresholds increased with retinal eccentricity and directional variance (noise), independent of acuity. Psychophysical modeling indicated that the results for eccentricity and noise could be explained by an increase in channel bandwidth and an increase in internal multiplicative noise.     

Modeling: An analysis in terms of category accessibility

It is proposed that many of the releasing or disinhibiting effects caused by models can be accounted for by information-processing mechanisms, without recourse to the concept of reinforcement. More specifically, it is suggested that the process of viewing a model's behavior involves the activation of an interpretive schema. This renders the information the schema incorporates more accessible for subsequent use. If the schema incorporates (or is closely related to) behavior-specifying information, that information becomes more accessible as well, thus making it more likely to influence overt behavior. Two studies are reported that assessed the plausibility of this reasoning. In Experiment 1 subjects who had viewed an aggressive model perceived greater hostility in the behavior of an ambiguous stimulus person that they subsequently encountered than did control subjects. This finding is consistent with the assumption that the model's behavior activated a conceptual schema for use in interpretation. In Experiment 2 subjects in whom an aggressive schema had been activated under a guise displayed greater aggression in their subsequent behavior in a different context than did control subjects. This finding is consistent with the assumption that activating the conceptual schema also activated behavioral information. The discussion centers on the implications of the findings.     

Effects of prime and target eccentricity on masked repetition priming

Three experiments examined the influence of briefly presented, pattern-masked prime stimuli on target word recognition at varying eccentricities. The prime was either the same word as the targets or a different word, and prime position varied horizontally from a central fixation point. The targets were either in the same location as the primes (Experiment 1A) or always centrally located (Experiments 1B and 2). In Experiment 1A, target word recognition showed a typical right visual field advantage, and priming effects diminished with increasing prime and target eccentricity. With centrally located targets, priming effects tended to be more constrained by prime location. After eye fixation location and prime visibility were controlled for (Experiment 2), a right visual field advantage for priming effects was also evident for central targets, suggesting an influence of endogenous attentional biases in masked repetition priming.     

Interaction of stimulus size and retinal eccentricity in metacontrast masking

Metacontrast masking occurs both at the fovea and in the retinal periphery; foveally, the smallest stimulus elicited the strongest masking, whereas peripherally the reverse was the case. An analysis of variance showed a significant size effect, eccentricity effect, and size-eccentricity interaction. As stimulus size increased, the stimulus onset asynchrony of maximum masking shifted to greater values. Both foveal metacontrast and peak shifts contradicted predictions made by the hypothesis that metacontrast is mediated by an interaction of sustained and transient channels in the visual system. The data are consistent, however, with a lateral inhibitory model of metacontrast masking and stimulus coding.     

Visual acuity in the pigeon II: effects of target distance and retinal lesions

Visual acuity thresholds for grating targets were determined for three pigeons at target distances ranging from 13 to 73 cm. These measurements were made both while the birds were wearing goggles restricting vision to the frontal field of view and when vision was unrestricted. Using a slightly different method, performance was also compared for target distances of 6 and 13 cm while the goggles were in place. For a second group of three pigeons, acuity data were obtained before and after laser lesions of the retina's foveal region. The findings suggested that acuity was relatively poor for targets at the intermediate distances and that it improved as distance both increased and decreased from these intermediate values. The acuity improvement with increasing distance did not occur, however, when the birds were wearing frontal goggles. The data appear to be consistent with Catania's 1964 suggestion that the pigeon has separate frontal and lateral visual systems that differ in their refractive characteristics. Foveal lesions did not appear to affect acuity for distant targets, and it was concluded that, while the fovea serves the lateral field of view, its presence is not necessary to the static acuity characteristics of this system.     

A reversal in the direction of detection asymmetry: effects of spatial density,spatial regularity,and retinal eccentricity

We analyzed detection asymmetry, using openand closed squares as target and contextelements. It was found that varying density, regularity, and target eccentricity not only can modulate the amount of asymmetry, but also can produce a reversal in the direction of the asymmetry. The results suggest that the different stimuli are processed with different grains of analysis,consisting of in some cases, single elements and their properties and, in other cases, larger units of the stimulus array and more globalproperties. A detection task that can utilize the properties that are available with a given grain of analysis would show an advantage over a task for which the given grain of analysis is not as favorable, resulting indetection asymmetry in one direction or another.     

Saccade latency in children and adults: Effects of warning interval and target eccentricity

Saccadic response latency to the onset of an eccentric target was studied in children (mean age = 8.7) and adults. The independent variables investigated were fixation-light offset to target-light onset warning interval (0, 100, 300, and 600 msec) and target eccentricity (5° or 15°). Both children and adults showed shorter saccade latencies under warning-interval conditions. Children were found to have longer latencies than adults with 0 or 100 msec warning intervals but to respond with as short or shorter latencies with 300 or 600 msec warning intervals. Target eccentricity effects did not interact with age, and occurred only with a lower target intensity. Children defined as poor readers could initiate a response as quickly as good readers but were less able to maintain fixation-light fixation prior to target onset.     

The latencies of correct and incorrect responses in discrimination and detection tasks: Their interpretation in terms of a model based on simple counting

A model for two-choice discrimination based on a process of simple counting is described, and two experiments are performed to test the predictions of the model concerning the graph of latency as a function of response proportion. Two main forms of this graph are identified and predicted to arise in different circumstances. The experimental results support the model, and its possible extension to other psychophysical situations, especially signal detection, are then discussed. It is compared with a model derived directly from the detection situation, and the usefulness of testing these models is pointed out.     

Detecting a target letter in briefly presented arrays: A confidence rating analysis in terms of a weighted additive effects model

A visual experiment is reported in which Os rated their “confidence” that briefly presented four-letter arrays contained one or more target-letter Fs. Their responses are interpreted as the product of a weighted “additive” combination of partial or “noisy” subjective representations of the four letters in each array.     

State-trace analysis of the effects of a visual illusion on saccade amplitudes and perceptual judgments

Visual illusions often appear to have a larger influence on subjective judgments than on visuomotor behavior. Although this effect has been taken as evidence for multiple estimates of stimulus size in the visual brain, dissociations between subjective judgments and visuomotor measures can frequently be reconciled with a singleestimate model. To circumvent this difficulty, we used state-trace analysis in a pair of experiments to examine the effects of the Müller-Lyer illusion on subjective length estimates, voluntary saccade amplitudes, and reflexive saccade amplitudes. All dependent measures were affected by the illusion. However, state-trace analyses revealed nonmonotonic relationships among all three variables, a pattern inconsistent with the possibility of a single underlying estimate of stimulus size.     

An account of consciousness in physical and functional terms: A target for research in the neurosciences

The neurophysiology of mental events cannot be fully understood unless that of consciousness is understood. As the first step in a top-down approach to that problem, one needs to find an account of consciousness as a property of the biological organism that can be clearly defined as such. However, if it is to deliver what must be expected of it, it should address what is commonly meant by the wordconsciousness. Unless the last condition is satisfied, the theory will fail to deliver what must ultimately be expected of it. Although current interest lies mainly in the higher functions of consciousness, such as its role in language and social relationships, the common usage of the word relates to modes of awareness that are not denied to creatures lacking language or social relationships. The basic features to be covered include awareness of the surrounding world, of the self, and of one’s thoughts and feelings; the subjective qualities of phenomenal experience (qualia); the conditions a brain event must satisfy to enter consciousness; and the main divisions of mental events, such as sensations, feelings, perceptions, desires, volitions, and mental images.     

The effects of advance location cueing on latencies in a single-letter recognition task

Summary This study investigates facilitating effects of foreknowledge of position in single-letter recognition tasks with latency as the dependent variable. Three kinds of cue are used: symbolic cues, location cues and neutral cues. For the effects of symbolic and location cues the following predictions are derived from the literature: increasing benefits with increasing SOAs for symbolic cues and constant benefits with increasing SOAs for location cues.Cue-detection times and letter-recognition times with the different cues were determined in three experiments. In the experiments the same general paradigm was used. In Experiment 1 cue-detection times appeared to differ as a function of cue eccentricity; in Experiments 2 and 3 cues were adjusted in such a way that cue-detection times were about the same. Cues reliably indicated the target position in Experiments 1 and 2; in Experiment 3 cue validity was reduced to 50%.The cueing results conformed partly to the predictions. All experiments suggested a small benefit under symbolic cueing and a larger benefit under location cueing. Except for the smallest SOA used, for both types of cue benefits were invariant over SOAs. The implications of these results in relation to other single-letter recognition studies are briefly discussed.     

The role of the saccade target object in the perception of a visually stable world

Although the proximal stimulus shifts position on our retinae with each saccade, we perceive our world as stable and continuous. Most theories of visual stability implicitly assume a mechanism that spatially adjusts perceived locations associated with the retinal array by using, as a parameter, extra-retinal eye position information, a signal that encodes the size and direction of the saccade. The results from the experiment reported in this article challenge this idea. During a participant's saccade to a target object, one of the following was displaced: the entire scene, the target object, or the background behind the target object. Participants detected the displacement of the target object twice as frequently as the displacement of the entire background. The direction of displacement relative to the saccade also affected detectability. We use a new theory, the saccade target theory (McConkie & Currie, 1996), to interpret these results. This theory proposes that retinal (as opposed to extra-retinal) factors, primarily those concerning the saccade target object, are critical for the detection of intrasaccadic stimulus shifts.