Experiments are described in which the subjects had to localize brief light stimuli presented up to 10 degrees from the fixation center. The localization was performed relative to a continuously illuminated scale with numbered or lettered divisions. Systematic errors were obtained, the stimuli being mislocated nearer the fixation point than they were actually presented. The angular size of errors increased with the increase of stimulus eccentricity. It appeared to be a characteristic of the stimulated retinal locus, independent of the viewing distance and the scale element corresponding to this locus. It is concluded that despite the presence of a visible background frame of reference, subjects prefer to base their reports on the perceived egocentric direction of the stimulus which does not coincide with the physical direction of the stimulus. A parallel is drawn between this study and the studies on serial position function for letter identification.

Visual localization phenomena were studied before, during, and after a saccade. Light flashes of .5 and 9 msec duration presented before and during the eye movement were mislocated in the saccade direction, the localization error being a time function. When the 9-msec duration stimulus and saccade did not overlap in time, a stripe was reported, when they did not, the stimulus was perceived as a point. If a long-duration stimulus moved perpendicularly to the saccade direction with the same "sigmoidal" velocity, a curvilinear trace was perceived, regardless of the linear trace of the image on the retina. A stimulus with stabilized retinal image was perceived as a stationary point during the saccade. A possible theory to deal with the data was suggested by modifying the algebra of outflow-inflow theories.When a visual stimulus is presented, one of the tasks presented to our visual system is to answer the question, "Where is it?" Our everyday experience shows this task to be performed relatively well. What is more, usually we localize surrounding objects properly, no matter where we look. In spite of the fact that a shift of gaze results in changes of the loci of the retinal image, under normal conditions object localization remains constant. This property of the visual system is known as "position constancy."Two of the explanations of position constancy are provided by the outflow and inflow theories, which are described briefly as follows. A center, or mechanism, which receives two "messages" is assumed to exist in the visual system. The first of these "messages" concerns the locus of the retinal image. The second provides information about the position of the eye. These two "messages" are somehow summated algebraically, and the resultant of this operation determines the perceived locus of the object. The difference between the two theories concerns the source of the information about eye position. According to the outflow theory (Holst, 1954;Holst & Mittelstaedt, 1950), this "message" comes from a hypothetical neural center from which the command to turn the eye originates, and it is thought that the "message" is a copy of the command for the eye movement. According to the alternative inflow theory (Sherrington, 1918), eye muscle proprioception provides this information.We will not deal with the outflow-inflow controversy in the present paper. The fact of importance for us is that both theories imply the same algebraic operations between information about the retinal locus of the object and about position of the eye. Thus, we shall consider them as one theory and call it "subtraction theory."Several authors (Bischof & Kramer, 1968;Matin, 1972;Matin & Matin, 1972; Matin, Matin, &Pearce, 1969;Matin, Matin, & Pola, 1970; Matin & Pearce, 1965;Monahan, 1972) have shown that a brief light stimulus presented during or just before voluntary saccadic eye movements is frequently mislocated by considerable amounts. The size of the error depends on the time at which the stimulus is presented relative to the saccade onset.M...

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Apparent motion of a sound source can be induced by a moving visual target. The direction of the perceived motion of the sound source is the same as that of the visual target, but the subjective velocity of the sound source is 25-50% of that of the visual target measured under the same conditions. Eye tracking of the light target tends to enhance the apparent motion of the sound, but is not a prerequisite for its occurrence. The findings are discussed in connection with the 'visual capture' or 'ventriloquism' effect.

Researchers have obtained similar results from different visual motion extrapolation experiments despite the large variety of motion stimuli used. With respect to the ability of human subjects to judge the moment at which an occluded moving stimulus arrives at a predetermined position along its motion path, the general conclusion has been that errors increase with the duration of the occluded motion. However, substantial individual differences are often obscured within this statement. We propose a linear model to describe the performance of human observers in motion extrapolation tasks. The results from an experiment on centrifugal and centripetal motion extrapolation are examined in terms of this model. We discuss the restrictions imposed by the model on conclusions drawn after converting estimated arrival times to velocity estimates or accuracy scores. The parameters of the linear regression describing the individual performance in motion extrapolation tasks might be appropriate measures of interindividual differences.