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Biomedical subjects

G W McConkie

Publications and source records attributed to G W McConkie.

15 recordsLinked to original sources
PubMed2001

Eye movements during reading: a theory of saccade initiation times.

As people read continuous text, on occasional single eye fixations the text was replaced by one of six alternate stimulus patterns. Frequency distributions of the durations of these fixations were used to test predictions from four types of theories of saccadic eye movement control. Contrary to current cognitive theories, cognitive influences appeared to delay saccades rather than trigger them. Two saccade disruption times were identified, suggesting the existence of three distributions of saccades, labeled early, normal and late. The Competition-inhibition theory, an enhanced version of Findlay and Walker's (1999) theory, is proposed to account for eye movement control during reading.

Adult↗
PubMed2001

Fixation location effects on fixation durations during reading: an inverted optimal viewing position effect.

Previous research has found that words are identified most quickly when the eyes are near their center (the Optimal Viewing Position effect). A study was conducted to determine whether this same phenomenon is observed during reading, as revealed by a relationship between fixation position in a word and the duration of the fixation. An analysis of three large existing corpora of eye movement data, two from adults and one from children, showed a surprising inverted Optimal Viewing Position curve: mean fixation duration is greatest, rather than lowest, when the eyes were at the centers of words. From this phenomenon, we suggest an alternative explanation to the fixation duration trade-off effect in word refixations [O'Regan & Lévy-Schoen, Attention and performance XII: the psychology of reading (1987)]; the phenomenon also contradicts expectations of both oculomotor and cognitive theories of eye movement control. Attempts to test alternative explanations led to the discovery of another phenomenon, the Saccade Distance effect: mean fixation durations vary with the distance of the prior fixation from the currently-fixated word, being longer with greater distances. The durations of fixations in reading are complexly determined, with influences both from language and perceptual/oculomotor levels.

Adult↗
PubMed2000

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.

Fixation, Ocular↗
PubMed1999

Attention to facial regions in segmental and prosodic visual speech perception tasks.

Two experiments were conducted to test the hypothesis that visual information related to segmental versus prosodic aspects of speech is distributed differently on the face of the talker. In the first experiment, eye gaze was monitored for 12 observers with normal hearing. Participants made decisions about segmental and prosodic categories for utterances presented without sound. The first experiment found that observers spend more time looking at and direct more gazes toward the upper part of the talker's face in making decisions about intonation patterns than about the words being spoken. The second experiment tested the Gaze Direction Assumption underlying Experiment 1--that is, that people direct their gaze to the stimulus region containing information required for their task. In this experiment, 18 observers with normal hearing made decisions about segmental and prosodic categories under conditions in which face motion was restricted to selected areas of the face. The results indicate that information in the upper part of the talker's face is more critical for intonation pattern decisions than for decisions about word segments or primary sentence stress, thus supporting the Gaze Direction Assumption. Visual speech perception proficiency requires learning where to direct visual attention for cues related to different aspects of speech.

Adult↗
PubMed1996

Visual stability across saccades while viewing complex pictures.

As people examine their world, the proximal stimulus changes position on their retinae with every saccade, but they perceive the world as being stable. This phenomenon of visual stability was explored by making changes in natural, full-color pictures during selected saccades as observers examined them in preparation for a recognition test. In Experiment 1, the pictures were displaced up, down, left, or right by 0.3, 0.4, or 1.2 degrees. In Experiment 2, the pictures were expanded or contracted by 10% or 20%. As a secondary task, subjects pressed a button when a change was detected. Three results from previous studies with simpler stimuli did not generalize. Evidence suggests that subjects' detection of image changes primarily involves the use of local information in the region of the eyes' landing position. A saccade target theory of visual stability is proposed.

Attention↗
PubMed1989

Eye movement control during reading: II. Frequency of refixating a word.

An analysis of over 40,000 eye fixations made by college students during reading indicates that the frequency of immediately refixating a word following an initial eye fixation on it varies with the location of that fixation. The refixation frequency is lowest near the center of the word, positively accelerating with distance from the center. The data are well fit by a parabolic function. Assuming that refixation frequency is related to the frequency of successful word identification, the observed curvilinear relation results naturally from models that postulate a linear decrease in visual information with retinal eccentricity. A single letter difference in fixation location in a word can make a sizeable difference in the likelihood of refixating that word. The effects of word length and cultural frequency on the frequency of refixating are also examined.

Adult↗
PubMed1988

Eye movement control during reading: I. The location of initial eye fixations on words.

Sixty-six college students read two chapters from a contemporary novel while their eye movements were monitored. The eye movement data were analyzed to identify factors that influence the location of a reader's initial eye fixation on a word. When the data were partitioned according to the location of the prior fixation (i.e. launch site), the distribution of fixation locations on the word (i.e. landing site distribution) was highly constrained, normal in shape, and not influenced by word length. The locations of initial fixations on words can be accounted for on the basis of five principles of perceptuo-oculomotor control: a word-object has a specific functional target location, a saccadic range error occurs that produces a systematic deviation of landing sites from the functional target location, the saccadic range error is reduced somewhat for saccades that follow longer eye fixations, there exists perceptuo-oculomotor variability that is a second, nonsystematic source of variation in landing sites, and the perceptuo-oculomotor variability increases with distance of the launch site from the target.

Eye Movements↗
PubMed1985

Some temporal characteristics of processing during reading.

College students read passages displayed on a cathode-ray tube as their eye movements were being monitored. During occasional fixations, all letters to the left of the directly fixated letter or all letters more than four to the right of the fixated letter were replaced by other letters. This replacement occurred either for only the first 100 ms of the fixation or only after the first 100 ms of the fixation. The eye movement data indicated that the eyes can respond to change in the visual stimulus within less than 100 ms and to orthographic irregularity in the text within less than 160 ms. No evidence was found for a left-to-right attentional scan during a fixation. The results were interpreted within the framework of a chronology of processing events occurring during a fixation in reading.

Attention↗
PubMed1984

Time course of visual information utilization during fixations in reading.

College students read short texts from a cathode-ray tube as their eye movements were being monitored. During selected fixations, the text was briefly masked and then it reappeared with one word changed. Subjects often were unaware that the word had changed. Sometimes they reported seeing the first presented word, sometimes the second presented word, and sometimes both. When only one word was reported, two factors were found to determine which one it was: the length of time a word was present during the fixation and the predictability of a word in its context. The results suggested that visual information is utilized for reading at a crucial period during the fixation and that this crucial period can occur at different times on different fixations. The pattern of responses suggested that the first letter of a word is not utilized before other letters and that letters are not scanned from left to right during a fixation.

Adult↗
PubMed1978

Eye movements and integrating information across fixations.

A series of experiments was conducted in which a word or letter string initially appeared in parafoveal vision, followed by the subject's eye movement to the stimulus. During the saccade, the initially displayed stimulus was replaced by a word that the subject was asked to read. The results indicated that the types of prior parafoveal information studied facilitated the naming of the word. The effect was obtained when the subject made an eye movement and when the saccade was simulated. There was also evidence that attentional allocation was tied to the direction of the eye movement.

Eye Movements↗