Toward a model of eye movement control in reading

The authors present several versions of a general model, titled the E-Z Reader model, of eye movement control in reading. The major goal of the modeling is to relate cognitive processing (specifically aspects of lexical access) to eye movements in reading. The earliest and simplest versions of the model (E-Z Readers 1 and 2) merely attempt to explain the total time spent on a word before moving forward (the gaze duration) and the probability of fixating a word; later versions (E-Z Readers 3-5) also attempt to explain the durations of individual fixations on individual words and the number of fixations on individual words. The final version (E-Z Reader 5) appears to be psychologically plausible and gives a good account of many phenomena in reading. It is also a good tool for analyzing eye movement data in reading. Limitations of the model and directions for future research are also discussed.     

Initial scene representations facilitate eye movement guidance in visual search.

What role does the initial glimpse of a scene play in subsequent eye movement guidance? In 4 experiments, a brief scene preview was followed by object search through the scene via a small moving window that was tied to fixation position. Experiment 1 demonstrated that the scene preview resulted in more efficient eye movements compared with a control preview. Experiments 2 and 3 showed that this scene preview benefit was not due to the conceptual category of the scene or identification of the target object in the preview. Experiment 4 demonstrated that the scene preview benefit was unaffected by changing the size of the scene from preview to search. Taken together, the results suggest that an abstract (size invariant) visual representation is generated in an initial scene glimpse and that this representation can be retained in memory and used to guide subsequent eye movements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is eye movement dysfunction a biological marker for schizophrenia? A methodological review.

There is a high prevalence of eye movement dysfunction (EMD) in persons with schizophrenia and their first-degree relatives. Studies addressing the prevalence, stability, familial transmission, and psychological correlates of EMD in persons from both psychiatric and general populations offer suggestive evidence that this abnormality may serve as a biological marker for schizophrenia. Although these findings are promising, their significance for elucidating the diagnostic bandwidth, pathophysiology, and genetics of this disorder remains to be determined. More precise characterization of ocular motility, perhaps when used in conjunction with global measures of pursuit adequacy, may be essential for clarifying the pathophysiological and genetic significance of EMD for schizophrenia. Recent research efforts are beginning to identify particular abnormalities that could serve as more specific biological markers for schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Directional organization of eye movement and visual signals in the floccular lobe of the monkey cerebellum

The floccular lobe of the monkey is critical for the generation of visually-guided smooth eye movements. The present experiments reveal physiological correlates of the directional organization in the primate floccular lobe by examining the selectivity for direction of eye motion and visual stimulation in the firing of individual Purkinje cells (PCs) and mossy fibers. During tracking of sinusoidal target motion along different axes in the frontoparallel plane, PCs fell into two classes based on the axis that caused the largest modulation of simple-spike firing rate. For "horizontal" PCs, the response was maximal during horizontal eye movements, with increases in firing rate during pursuit toward the side of recording (ipsiversive). For "vertical" PCs, the response was maximal during eye movement along an axis just off pure vertical, with increases in firing rate during pursuit directed downward and slightly contraversive. During pursuit of target motion at constant velocity, PCs again fell into horizontal and vertical classes that matched the results from sinusoidal tracking. In addition, the directional tuning of the sustained "eye velocity" and transient "visual" components of the neural responses obtained during constant velocity tracking were very similar. PCs displayed very broad tuning approximating a cosine tuning curve; the mean half-maximum bandwidth of their tuning curves was 170-180 degrees. Other cerebellar elements, related purely to eye movement and presumed to be mossy fibers, exhibited tuning approximately 40 degrees narrower than PCs and had best directions that clustered around the four cardinal directions. Our data indicate that the motion signals encoded by PCs in the monkey floccular lobe are segregated into channels that are consistent with a coordinate system defined by the vestibular apparatus and eye muscles. The differences between the tuning properties exhibited by PCs compared with mossy fibers indicate that a spatial transformation occurs within the floccular lobe.     

Increased dependence on visual information for movement control in patients with Parkinson's disease

Studies were made of visually and non-visually guided movements by patients with Parkinson's disease. The subjects moved a light, horizontal handle using rotation primarily about the elbow. During visually guided trials both handle and target positions were displayed to the subject; during non-visually guided trials only the handle position was displayed. During non-visually guided trials all patients showed a tendency for an overall flexion drift, although there was no change in average movement amplitude. The overall error in position by the end of the non-visually guided trials was greatly in excess of the reported values for passive displacement thresholds in normal subjects. It is suggested that the data indicate an increased dependence on visual information for control of motor activity in Parkinson's patients.     

Unspaced text interferes with both word identification and eye movement control

Subjects read either normal text, text in which the space information between words was absent (either spaces were removed filled with x), or text in which spaces were preserved but the words were flanked by x. In two experiments, reading rate decreased by approx. 50% when space information was not available, suggesting that reading unspaced text is relatively difficult. The removal of space information increased the effect of word frequency on the fixation times for selected target words, indicating that word identification was interfered with by the lack of spaces. In addition, removal of space information influenced the initial landing positions on words, indicating that eye movement control was affected by the absence of spaces. Further analyses were conducted that explored the relationship between these two effects.     

Is consistent mapping necessary for high-speed search?

Recent research has suggested that visual-search functions will become shallower with practice, but only if the stimuli and responses are consistently mapped. We tested the necessity of consistent mapping for the phenomenon by asking subjects to report the largest digit in a visual display. Despite the fact that we used a varied-mapping task, significant reduction in the visual search function was observed. The reduction could not be attributed to the probability information in the task. Perfectly consistent mapping of stimulus to response does not appear to be a necessary precondition for reduction of visual-search rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A neural model of multimodal adaptive saccadic eye movement control by superior colliculus

How does the saccadic movement system select a target when visual, auditory, and planned movement commands differ? How do retinal, head-centered, and motor error coordinates interact during the selection process? Recent data on superior colliculus (SC) reveal a spreading wave of activation across buildup cells the peak activity of which covaries with the current gaze error. In contrast, the locus of peak activity remains constant at burst cells, whereas their activity level decays with residual gaze error. A neural model answers these questions and simulates burst and buildup responses in visual, overlap, memory, and gap tasks. The model also simulates data on multimodal enhancement and suppression of activity in the deeper SC layers and suggests a functional role for NMDA receptors in this region. In particular, the model suggests how auditory and planned saccadic target positions become aligned and compete with visually reactive target positions to select a movement command. For this to occur, a transformation between auditory and planned head-centered representations and a retinotopic target representation is learned. Burst cells in the model generate teaching signals to the spreading wave layer. Spreading waves are produced by corollary discharges that render planned and visually reactive targets dimensionally consistent and enable them to compete for attention to generate a movement command in motor error coordinates. The attentional selection process also helps to stabilize the map-learning process. The model functionally interprets cells in the superior colliculus, frontal eye field, parietal cortex, mesencephalic reticular formation, paramedian pontine reticular formation, and substantia nigra pars reticulata.     

Evaluation of vestibular and visual oculomotor function

The visual system interacts synergistically with the vestibular system. A normally functioning vestibulo-ocular reflex is necessary but not sufficient for optimum visual acuity during head motion. Studies of dynamic visual acuity, the acuity achieved during relative motion of visual targets or of the observer, indicate that motion of images on the retina markedly compromises vision. The vestibulo-ocular reflex normally provides a substantial measure of stabilization of the retina during head movements, but purely vestibular compensatory eye movements are not sufficiently precise for optimal vision under all circumstances. Other mechanisms, including visual tracking, motor preprogramming, prediction, and mental set, interact synergistically to optimize the gain (eye velocity divided by head velocity) of compensatory head movements. All of these mechanisms are limited in their capacity to produce effective visual-vestibular interaction at higher rotational frequencies and velocities. It is under these conditions that vestibular deficits give rise to symptoms of oscillopsia. Patients having vestibular lesions exploit mechanisms of visual-vestibular interaction to compensate by substitution for deficient vestibular function. Thus, for accurate topographic clinical diagnosis of vestibular lesions, testing conditions should isolate purely vestibular responses. This may be done by testing reflex eye movements during passively generated rotations in darkness, or perhaps by testing during other types of motion under conditions of extreme frequency and velocity sufficient to attenuate the effects of visual-vestibular interaction. This article reviews clinical tests of vestibular function in relation to synergistic interactions with vision.     

The directional effects of passive eye movement on the directional visual responses of single units in the pigeon optic tectum

We have investigated the visual responses of 184 single units located in the superficial layers of the optic tectum (OT) of the decerebrate, paralysed pigeon. Visual responses were similar to those reported in non-decerebrate preparations; most units responded best to moving visual stimuli, 18% were directionally selective (they had a clear preference for a particular direction of visual stimulus movement), 76% were plane-selective (they responded to movement in either direction in a particular plane). However, we also found that a high proportion of units showed some sensitivity to the orientation of visual stimuli. We examined the effects of extraocular muscle (EOM) afferent signals, induced by passive eye movement (PEM), on the directional visual responses of units. Visual responses were most modified by particular directions of eye movement, although there was no unique relationship between the direction of visual stimulus movement to which an individual unit responded best and the direction of eye movement that caused the greatest modification of that visual response. The results show that EOM afferent signals, carrying information concerning the direction of eye movement, reach the superficial layers of the OT in the pigeon and there modify the visual responses of units in a manner that suggests some role for these signals in the processing of visual information.     

Is love a necessary ingredient for sexual fulfilment?

Sexual intercourse and orgasm are regarded as a significant but not fundamental aspect of marital fulfillment. True sexual fulfillment arises from possessing and being possessed in a matrimonial state and can thus only exist in a stable and enduring marriage. Those who indulge in premarital intercourse, adultery, and masturbation for personal satisfaction will find such experiences shallow. Contraception is described as an act of violence against the natural reproductive process and as such, an act that cannot possibly foster love. Contraceptive intercourse is thought to be behind many marital breakdowns. The author acknowledges that his philosophy will on occasion lead to rearing a quite large family but feels such a family can provide a tremendous amount of love, satisfaction, and fulfillment, given that tasks involved are shared.     

Effects of foveal processing difficulty on the perceptual span in reading: Implications for attention and eye movement control.

Two experiments were conducted to examine the effects of foveal processing difficulty on the perceptual span in reading. Subjects read sentences while their eye movements were recorded. By changing the text contingent on the reader's current point of fixation, foveal processing difficulty and the availability of parafoveal word information were independently manipulated. In Experiment 1, foveal processing difficulty was manipulated by lexical frequency, and in Experiment 2 foveal difficulty was manipulated by syntactic complexity. In both experiments, less parafoveal information was acquired when processing in the fovea was difficult. We conclude that the perceptual span is variable and attentionally constrained. We also discuss the implications of the results for current models of the relation between covert visual–spatial attention and eye movement control in reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biases in visual orienting to negative and positive scenes in dysphoria: An eye movement study.

The study investigated biases for negative information in component processes of visual attention (initial shift vs. maintenance of gaze) in dysphoric and nondysphoric individuals. Eye movements were recorded while participants viewed a series of picture pairs depicting negative, positive, and neutral scenes (each pair presented for 3 s). Biases in initial orienting were assessed from the direction and latency of the initial shift in gaze, whereas biases in the maintenance of attention were assessed from the duration of gaze on the picture that was initially fixated. Results indicated that the dysphoric group showed a significantly greater bias to maintain gaze longer on negative pictures, relative to control pictures, compared with the nondysphoric group. There was no evidence of a dysphoria-related bias in initial shift of orienting to negative cues. Results are consistent with a depression-related bias that operates in the maintenance of attention on negative material. (PsycINFO Database Record (c) 2010 APA, all rights reserved)