Search performance without eye movements

Visual search performance (with sets chosen to elicit both serial and parallel search patterns) under two conditions that precluded saccades was compared to the typical situation in which visual inspection of the array is possible. In one condition, the display duration was so brief that any saccades that were executed would be too late to bring the targeted portion of the array into the fovea. In the other, the display remained present until the subject's response, but eye position was monitored and trials with shifts in fixation were excluded from analysis. The latter condition produced search latencies that were nearly identical to those with free inspection. Brief exposure, in contrast, did not produce the pattern typical of serial search, presumably because of strategies induced to deal with the rapid decay of the visual array. It is concluded that saccadic eye movements play little role in the patterns of performance used to infer serial and parallel search, and that brief exposure is not a satisfactory technique for exploring the role of saccadic eye movements in visual search.     

Integration of form across saccadic eye movements.

To perceive a stable world, one must somehow be able to relate visual information from successive fixations. Little is known, however, about the nature of the integrative process. By using a task which requires the integration of spatial position information from different fixations, it is demonstrated that visual information from previous fixations is preserved in a world-centered representation which is precise enough to support judgements of geometric shape. It is also shown that successive views are aligned with respect to common visual features, indicating that visual stability may be normally accomplished by a visual matching strategy in combination with cancellation by an eye-position signal.     

Selective eye movements to simultaneously presented stimuli during discrimination

Human Ss, when given a discrimination task whose stimuli varied in dimension and relevance, always chose and ftxated more frequently the stimulus they had been reinforced for choosing. Decreasing the brightness reduced the choice and ftxation preference for form stimuli over line stimuli and raised total ftxation frequency. Ss decreased fixation frequency to discriminanda with practice.     

Tracking without perceiving: a dissociation between eye movements and motion perception

Can people react to objects in their visual field that they do not consciously perceive? We investigated how visual perception and motor action respond to moving objects whose visibility is reduced, and we found a dissociation between motion processing for perception and for action. We compared motion perception and eye movements evoked by two orthogonally drifting gratings, each presented separately to a different eye. The strength of each monocular grating was manipulated by inducing adaptation to one grating prior to the presentation of both gratings. Reflexive eye movements tracked the vector average of both gratings (pattern motion) even though perceptual responses followed one motion direction exclusively (component motion). Observers almost never perceived pattern motion. This dissociation implies the existence of visual-motion signals that guide eye movements in the absence of a corresponding conscious percept.     

Attention and generalization during a conditional discrimination

A conditional discrimination was established and analyzed, using four pigeons. The discrimination was among four compound stimuli projected on the response key—a white circle or triangle on a red or green background—during two conditions of illumination in the chamber, no illumination or flashing illumination. The two lighting conditions indicated whether the stimuli on the key containing triangles or those containing red would be the occasion for reinforcement. After the discrimination formed, generalization to intermediate and extreme values of the conditional stimulus and the attention of the birds to separate aspects of the stimulus on the key under each of the conditional stimuli were studied. All subjects generalized across values of the conditional stimulus, the lighting of the chamber. But subjects differed in the manner in which they treated the compound stimuli: two tended to attend to one or the other aspect of the stimulus on the key depending on the conditional stimulus, and two offered no evidence of such selective attention. Thus, the differential control of responding by the conditional stimuli cannot be attributed to a shift in attention between the figure and ground aspects of the compound stimuli.     

Typical predictive eye movements during action observation without effector-specific motor simulation

When watching someone reaching to grasp an object, we typically gaze at the object before the agent’s hand reaches it—that is, we make a “predictive eye movement” to the object. The received explanation is that predictive eye movements rely on a direct matching process, by which the observed action is mapped onto the motor representation of the same body movements in the observer’s brain. In this article, we report evidence that calls for a reexamination of this account. We recorded the eye movements of an individual born without arms (D.C.) while he watched an actor reaching for one of two different-sized objects with a power grasp, a precision grasp, or a closed fist. D.C. showed typical predictive eye movements modulated by the actor’s hand shape. This finding constitutes proof of concept that predictive eye movements during action observation can rely on visual and inferential processes, unaided by effector-specific motor simulation.     

Fixed-target efficient search has logarithmic efficiency with and without eye movements

Stage 1 processing in visual search (e.g., efficient search) has long been thought to be unaffected by factors such as set size or lure–distractor similarity (or at least to be only minimally affected). Recent research from Buetti, Cronin, Madison, Wang, and Lleras (Journal of Experimental Psychology: General, 145, 672–707, 2016) showed that in efficient visual search with a fixed target, reaction times increase logarithmically as a function of set size and, further, that the slope of these logarithmic functions is modulated by target–distractor similarity. This has led to the proposal that the cognitive architecture of Stage 1 processing is parallel, of unlimited capacity, and exhaustive in nature. Such an architecture produces reaction time functions that increase logarithmically with set size (as opposed to being unaffected by it). However, in the previous studies, eye movements were not monitored. It is thus possible that the logarithmicity of the reaction time functions emerged simply as an artifact of eye movements rather than as a reflection of the underlying cognitive architecture. Here we ruled out the possibility that eye movements resulted in the observed logarithmic functions, by asking participants to keep their eyes at fixation while completing fixed-target efficient visual search tasks. The logarithmic RT functions still emerged even when participants were not allowed to make eye movements, thus providing further support for our proposal. Additionally, we found that search efficiency is slightly improved when eye movements are restricted and lure–target similarity is relatively high.     

Calibration of peripheral perception of shape with and without saccadic eye movements

The cortical representations of a visual object differ radically across saccades. Several studies claim that the visual system adapts the peripheral percept to better match the subsequent foveal view. Recently, Herwig, Weiß, and Schneider (2015, Annals of the New York Academy of Sciences, 1339(1), 97–105) found that the perception of shape demonstrates a saccade-dependent learning effect. Here, we ask whether this learning actually requires saccades. We replicated Herwig et al.’s (2015) study and introduced a fixation condition. In a learning phase, participants were exposed to objects whose shape systematically changed during a saccade, or during a displacement from peripheral to foveal vision (without a saccade). In a subsequent test, objects were perceived as less (more) curved if they previously changed from more circular (triangular) in the periphery to more triangular (circular) in the fovea. Importantly, this pattern was seen both with and without saccades. We then tested whether a variable delay between the presentations of the peripheral and foveal objects would affect their association—hypothetically weakening it at longer delays. Again, we found that shape judgments depended on the changes experienced during the learning phase and that they were similar in both the saccade and fixation conditions. Surprisingly, they were not affected by the delay between the peripheral and foveal presentations over the range we tested. These results suggest that a general associative process, independent of saccade execution, contributes to the perception of shape across viewpoints.

     

Acquisition, generalization, and discrimination reversal of a natural concept

Pigeons rapidly acquired a discrimination between 40 pictures containing trees and 40 not containing trees. Differential reinforcement did not affect the discriminability of individual instances of trees. Generalization to new instances of tree pictures was better than to new instances of non-tree pictures. The level of discrimination did not depend on whether trees constituted the reinforced or the unreinforced category.     

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.     

Operant control of eye movements

In a monitoring situation eye movements were required in order for signals to be presented. Detection of signals was the reinforcement. A multiple schedule of fixed-interval reinforcement, differential reinforcement of low rate, and fixed-ratio reinforcement was established for eye movements. Results demonstrated that an eye movement can act as an operant controlled by its consequences. Operant control of eye movements has important implications for human factor analysts concerned with "attention".     

The influence of generalization decrement on the outcome of a feature-positive discrimination

In a feature-positive discrimination subjects receive training in which reinforced presentations of a compound, AB⁺, are intermixed among non-reinforced presentations of one element, A^o. The three reported experiments compared the results of this procedure when using a light or a tone as the feature-positive stimulus, B. In all three experiments, the tone elicited a stronger conditioned response than the light when it was presented alone. The main concern of Experiments 2 and 3 was to examine whether this effect was due to training being incomplete for subjects receiving the light as the B element. In Experiment 2 it was found that extended discrimination training did not diminish the difference between the properties of the light and the tone. Experiment 3 revealed that this effect was not due to differences in the asymptotic associative strength of either A or the compound. It is argued that these results are not readily compatible with contemporary theories of learning, and an alternative account is presented.