A VERSATILE EYE-MOVEMENT RECORDER

A small, light eye-movement recorder, capable of registering eye movements from the smallest voluntary movements to movements of 20 degrees of arc, is described. A miniature light projector gives a beam of infrared (or blue) light, which is reflected by the cornea of the eye. The beam is deflected by any movement of the eye. An optical system transforms the motion of the beam into changes of light intensity. These are translated into magnified fluctuations of current in a multiplier phototube. The output is translated into graphic form by an ink-writer fitted with a D.C. amplifier. The apparatus, except for the writer but including a helmet, weighs about 300–500 g and is mounted on the subject's head without appreciably disturbing the field of vision.     

Investigating the effects of inversion on configural processing with an audiovisual temporal-order judgment task

Research has shown that inversion is more detrimental to the perception of faces than to the perception of other types of visual stimuli. Inverting a face results in an impairment of configural information processing that leads to slowed early face processing and reduced accuracy when performance is tested in face recognition tasks. We investigated the effects of inverting speech and non-speech stimuli on audiovisual temporal perception. Upright and inverted audiovisual video clips of a person uttering syllables (experiments 1 and 2), playing musical notes on a piano (experiment 3), or a rhesus monkey producing vocalisations (experiment 4) were presented. Participants made unspeeded temporal-order judgments regarding which modality stream (auditory or visual) appeared to have been presented first. Inverting the visual stream did not have any effect on the sensitivity of temporal discrimination responses in any of the four experiments, thus implying that audiovisual temporal integration is resilient to the effects of orientation in the picture plane. By contrast, the point of subjective simultaneity differed significantly as a function of orientation only for the audiovisual speech stimuli but not for the non-speech stimuli or monkey calls. That is, smaller auditory leads were required for the inverted than for the upright-visual speech stimuli. These results are consistent with the longer processing latencies reported previously when human faces are inverted and demonstrates that the temporal perception of dynamic audiovisual speech can be modulated by changes in the physical properties of the visual speech (ie by changes in orientation).     

Simultaneous auditory discrimination.

Stimuli in many visual stimulus control studies typically are presented simultaneously; in contrast the stimuli in auditory discrimination studies are presented successively. Many everyday auditory stimuli that control responding occur simultaneously. This suggests that simultaneous auditory discriminations should be readily acquired. The purpose of the present experiment was to train rats in a simultaneous auditory discrimination. The apparatus consisted of a cage with two response levers mounted on one wall and a speaker mounted adjacent to each lever. A feeder was mounted on the opposite wall. In a go-right/go-left procedure, two stimuli were presented on each trial, a wide-band noise burst through one speaker and a 2-kHz complex signal through the other. The stimuli alternated randomly from side to side across trials, and the stimulus correlated with reinforcement for presses varied across subjects. The rats acquired the discrimination in 400 to 700 trials, and no response position preference developed during acquisition. The ease with which the simultaneous discrimination was acquired suggests that procedures, such as matching to sample, that require simultaneous presentation of stimuli can be used with auditory stimuli in animals having poor vision.     

Primate head and body restraint without chronic skin openings or attachments to the animal

We developed a primate restraint system that requires no chronic skin openings or attachments to the animal. The restraining chair has a unique neck clasp; monkeys without chains and collars are easily trained to readily enter the chair and accept restraint with the neck and head held at a comfortable angle. A bite bar, in combination with contact on broad areas of the monkey’s brow and occiput, provides rigid head immobilization. In order to achieve contact with a broad area of the occipital bone, the muscles at the back of the animal’s head are surgically detached from the occiput and reattached to the underlying neck muscles. A strain-gauge, mounted on the head-holder and monitored by a laboratory computer, detects head movements of the monkey and permits the experimenter to teach the monkey to sit still during data acquisition. This system is well accepted by experienced monkeys and helps prevent the risks of infection posed by most earlier methods. Furthermore, the head and shoulders of the monkey are readily accessible for examination and for close positioning of test equipment.     

Behavioral control of visual fixation of the rhesus monkey.

A paradigm for the control of visual fixation of the macaque monkey in vision experiments was described. Using a Maxwellian view, the procedure permits the placement of discrete test-light stimuli in a specific area of the retina as the monkey fixates a primary target. This procedure holds foveal fixation as other behaviorally significant visual stimuli are presented to the visual field. By a methods-of-limits procedure, the sensitivity of the monkey eye was measured at different retinal locations under both photopic and scotopic visual adaptation.     

Orientation Constancy in Neurons of Monkey Visual Cortex

We studied the effect of body tilt on the orientation selectivity of single neurons in the visual cortex of an alert monkey. The monkey performed a visual fixation task either in the upright position or with its whole body tilted about the naso-occipital (roll) axis by ±25° or ±30°. We determined the preferred stimulus orientation for 51 of 117 neurons in two or, if possible, three body positions (i.e. with the whole body upright, and tilted either left ear or right ear down). In striate cortex, most of the neurons were of a non-compensatory type, showing a change in the preferred orientation according to the body tilt and the estimated counterrolling of the eye. By contrast, about 40% of the neurons in prestriate cortex were of a compensatory type, preferring similar orientations in all body positions. This suggests that mechanisms which produce orientation constancy with respect to the direction of gravity are implemented at an early stage of cortical processing.     

Learning and limits of use of eye gaze by capuchin monkeys (Cebus apella) in an object-choice task

The ability of 3 capuchin monkeys (Cebus apella) to use experimenter-given cues to solve an object-choice task was assessed. The monkeys learned to use explicit gestural and postural cues and then progressed to using eye-gaze-only cues to solve the task, that is, to choose the baited 1 of 2 objects and thus obtain a food reward. Increasing cue-stimulus distance and introducing movement of the eyes impeded the establishment of effective eye-gaze reading. One monkey showed positive but imperfect transfer of use of eye gaze when a novel experimenter presented the cue. When head and eye orientation cues were presented simultaneously and in conflict, the monkeys showed greater responsiveness to head orientation cues. The results show that capuchin monkeys can learn to use eye gaze as a discriminative cue, but there was no-evidence for any underlying awareness of eye gaze as a cue to direction of attention.     

Face processing in humans and new world monkeys: the influence of experiential and ecological factors

This study tests whether the face-processing system of humans and a nonhuman primate species share characteristics that would allow for early and quick processing of socially salient stimuli: a sensitivity toward conspecific faces, a sensitivity toward highly practiced face stimuli, and an ability to generalize changes in the face that do not suggest a new identity, such as a face differently oriented. The look rates by adult tamarins and humans toward conspecific and other primate faces were examined to determine if these characteristics are shared. A visual paired comparison (VPC) task presented subjects with either a human face, chimpanzee face, tamarin face, or an object as a sample, and then a pair containing the previous stimulus and a novel stimulus was presented. The stimuli were either presented all in an upright orientation, or all in an inverted orientation. The novel stimulus in the pair was either an orientation change of the same face/object or a new example of the same type of face/object, and the stimuli were shown either in an upright orientation or in an inverted orientation. Preference to novelty scores revealed that humans attended most to novel individual human faces, and this effect decreased significantly if the stimuli were inverted. Tamarins showed preferential looking toward novel orientations of previously seen tamarin faces in the upright orientation, but not in an inverted orientation. Similarly, their preference to look longer at novel tamarin and human faces within the pair was reduced significantly with inverted stimuli. The results confirmed prior findings in humans that novel human faces generate more attention in the upright than in the inverted orientation. The monkeys also attended more to faces of conspecifics, but showed an inversion effect to orientation change in tamarin faces and to identity changes in tamarin and human faces. The results indicate configural processing restricted to particular kinds of primate faces by a New World monkey species, with configural processing influenced by life experience (human faces and tamarin faces) and specialized to process orientation changes specific to conspecific faces.     

Influence of background on precision of 3D depth judgment tasks in a real environment

Presently, little is known about the effect of curved backgrounds against which the target stimulus is presented on precision in stereoacuity. The experiment analyzed the influence of stimulus orientation and 3D background configuration on stereoscopic vision. Participants were instructed to perform 3D visual alignment tasks on a modified version of the Howard-Dolman apparatus, whereupon precision in depth perception for different curved backgrounds (flat, black, concave, and convex) was evaluated. In addition, the influence of stimulus orientation (0 degrees, 45 degrees, and 90 degrees) on precision was examined. The findings revealed an underestimation in the perceived depth in all background configurations, indicating highest and lowest precision outcomes for convex and concave backgrounds, respectively. In addition, a significant interaction of background and orientation was found. It was concluded that, in a real environment, background local depth cues are integrated with target stimuli to contribute to depth perception.     

Loss of wavelength selectivity in contour masking and aftereffect following dichoptic adaptation

Two experiments measured the apparent orientation (aftereffect) and the threshold for detection (masking) of a colored grating viewed by one eye after exposure to a colored grating to the same or the opposite eye (monoptic inspection) or after stimulation of one eye by color and the other eye by contours (dichoptic inspection). Under the monoptic condition, the color relationship between the inspection and test stimuli exerted control over the extent of aftereffect and masking when the two stimuli were viewed with the same eye, but not when they were seen with different eyes. Aftereffect and masking were nonselective to wavelength following dichoptic inspection, irrespective of whether the test stimulus was presented to the color-adapted or to the contour-adapted eye. The results support other claims that visual detectors with chromatic and spatial tuning have monocular specificity.     

A turn-key transportable eye-tracking instrument for clinical assessment

This paper describes a combined instrument (eye tracker and target generator, both head mounted, with integrated data analysis) that tests parameters of saccadic eye movement and fixation control to give insight into the status of functional brain systems. Using three minilasers, the target generator projects three visual stimuli, a fixation point and two lateral stimuli, with programmable timing. The controller allows the selection of overlap, 200-msec gap, or remembered saccade trials. Size, maximal velocity, and reaction time are determined for each primary saccade. The number of prosaccades and antisaccades are counted. More saccades—for example, the occurrence and latency of corrective saccades—may be evaluated off line by an interactive PC analysis program. The eye position data can be transferred to a PC. Off-line analysis compares each observed variable relative to an age-matched control group (300 healthy control subjects 7–70 years of age, tested in the overlap condition with prosaccade instructions and in the gap condition with antisaccades). The diagnostic results can be used to elaborate an individual optomotor training program.     

Dichoptic induction of Mccollough-type effects

If left-oblique and right-oblique black/white gratings are presented alternately to one eye, and unpatterned red and green fields are presented alternately to the other, orientation-sensitive chromatic after-effects are induced. With the colour-stimulated eye the hue usually seen on a test grating is complementary to that originally paired with its orientation, with the pattern-stimulated eye the hue is the same as that originally paired.

The experiments reported here show that: (a) the time course of decay of these chromatic after-effects (for each eye) fits approximately the same power law as that found for the normal McCollough effect; (b) analogous chromatic after-effects, opposite in the two eyes, can be dichoptically induced using pairs of stimuli other than gratings, such as dot patterns differing in magnification.

These results suggest that strongly coloured light in one eye can induce a weakly complementary bias in the colour-signalling system of the other eye, at a level peripheral to the site of the McCollough-type adaptation.     

Visual stimuli for strabismic suppression

The effects of orientation and spatial frequency of grating stimuli upon suppression were examined with a binocular rivalry paradigm in a group of ten strabismic patients and in a control normal group. Duration, frequency, and period of rivalry were examined as functions of differences in orientation and spatial frequency of dichoptic achromatic sinusoidal gratings. Records were made of responses by the sighting and by the nonsighting eye as well as responses during periods of combined binocular vision. Strabismic subjects reported normal binocular rivalry when presented with gratings of dissimilar orientation. Suppression of the deviating eye in strabismic subjects occurred with stimuli of similar orientation and was unaffected by spatial-frequency differences between dichoptic stimuli. Suppression was most intense under conditions that normally stimulate stereopsis and sensory fusion.     

Rate of response as a visual social stimulus

In Exp. 1, a high rate of responding (chain pulling) of a stimulus monkey was established as a visual positive discriminative stimulus for the operant behavior (bar pressing) of an observer monkey. The terminal performance of the observer under conditions in which a high rate of response of the stimulus monkey alternated in a variable temporal arrangement with a zero rate of response of the stimulus monkey (negative discriminative stimulus) was essentially the same as when nonbehavioral stimuli are correlated with the availability of reinforcement. By manipulating the schedule of reinforcement to change the rate of responding of the stimulus subject without changing its rate of reinforcement, Exp. 2 showed that the effective behavioral stimulus for the observer was the rate of chain pulling by the stimulus subject. A novel intermediate rate of responding by the stimulus monkey resulted in an intermediate rate (generalization) on the part of the observer during an extinction test. These experiments demonstrated that the rate of responding of one organism can function as a discriminative stimulus to control the rate of responding of another organism; and that the rate of responding is similar to other physical stimuli in terms of discrimination and generalization.     

Measurement of adult performance on Piaget's water horizontality task

Three versions of Piaget's water-level-horizontality task (multiple choice, drawing, and apparatus tests) were administered to 121 female and 74 male adult volunteers. Sex differences and container orientation effects were replicated. Men were more accurate than women and horizontal and vertical container orientations evoked more accurate responses than oblique orientation. Reliability estimates ranged from .78 to .97 and correlations among the measures ranged from .78 to .88. The relative merits of alternative water-level testing and scoring methods and the orientation and type of stimuli to be used are discussed.     

"Don't Ask, Don't Tell": The Influence of Stigma Concealing and Perceived Threat on Perceivers' Reactions to a Gay Target

This research examined reactions to a gay target who was either concealing or not concealing his sexual orientation under conditions of threat (HIV-positive) or no threat (healthy). When the target concealed his sexual orientation, participants were more willing to interact socially with him, but rated him as having more negative characteristics than when he was open about his sexual orientation. Participants rated a threatening target more negatively on a thermometer evaluation, perceived him to be more immoral, had more negative affective reactions, and desired more social distance than when the target was nonthreatening. The results are integrated with previous theoretical discussions and are considered in terms of the conflicting motivations of perceivers and targets.     

On-line monitoring of eye-position signals in contingent and noncontingent paradigms

This paper presents a research methodology for the study of human attentional and perceptual processes by means of on-line monitoring of eye-position signals. The first part of the presentation considers techniques by which commercially available apparatus may be interfaced to a minicomputer for purposes of monitoring eye-position signals during psychological experiments. Hardware and software techniques related to automating the calibration, recording, and analysis of eye-position data are discussed. The second part of the paper discusses a more advanced research methodology, one in which visual stimuli are contingent upon momentary eye-position signals. The methodology is appropriate to a variety of studies in which eye movements are considered to be part of an attentional control system. Several experimental applications are described. The implementation of eye-position-stimulus contingencies on a small computer poses additional technical problems, several of which are discussed.     

PERCEPTION OF MOTION AND CHANGING FORM: A study of visual perception from continuous transformations of a solid angle of light at the eye

It is shown how geometrically changing projections of objects which move and/or change their shape carry no specific information about form and three-dimensional motion. How, then, does the visual apparatus produce specific percepts from such non-specific changing stimuli? By applying an analogue computer technique, changing projections of artificial objects are generated on a CRT screen. These projections are fed into the eye by means of an optical device where they form a continuously changing solid angle of homogeneous light. The main conclusion is that it is a principle of perceptual three-dimensionality which gives specificity to the percepts. Preliminary statements of principles for prediction of perceived motion in depth from a given change in proximal stimulus are presented.     

The depth and selectivity of suppression in binocular rivalry

Binocular rivalry occurs when the two eyes are presented with incompatible stimuli and the perceived image alternates between the two stimuli. The aim of this study was to find out whether the periodic perceptual loss of a monocular stimulus during binocular rivalry is mirrored by a comparable loss of contrast sensitivity. We presented brief test stimuli to one eye while its conditioning stimulus was dominant or suppressed. The test stimuli were varied widely across four stimulus domains--namely, the relative stimulation of medium- and long-wavelength-sensitive cones, duration, spatial frequency, and grating orientation. The result in each case was the same. Suppression depended slightly or not at all on the type of test stimulus, and contrast sensitivity during suppression was around 64% of that during dominance. The effect of suppression on sensitivity is therefore very weak, relative to its effect on the perceived image. Furthermore, suppression was largely independent of the similarity between the conditioning and the test stimuli, indicating that our results are better explained by eye suppression than by stimulus suppression. A model is presented to account for the small, monocular sensitivity loss during suppression: It assumes that test detection precedes conditioning stimulus perception in the visual pathway.     

Orientation constancy of the McCollough effect

Two different techniques were used to determine the orientation constancy of orientation-contingent color aftereffects, McCollough effects. The results from both investigations agree and indicate That the aftereffect fails to exhibit orientation constancy other than that which can be explained by ocular countertorsion. Thus, the retinal rather than phenomenal orientation of the adaptation stimuli appears to be the determinant of aftereffect orientation. In fact, it is concluded that the aftereffect can be used to accurately monitor torsional eye position over long periods of time.