A new approach to the generation of visual stimuli for eye-movement research

An interactive, computer-controlled, visual stimulus generator is described, suitable for both psychophysical and neurophysiological experimentation on human subjects. The system core is a wide-screen electrostatic cathode-ray tube, which can be used both as a television monitor, to display standard video pictures, and as anx-y oscilloscope, so that a bright dot can be moved around the display by electrical signals. In addition, a third working mode is provided, according to which a time-compressed video picture of limited size (fast picture) plays the role that is typical of the spot in a standard oscilloscope. Through computer-assisted time compression, the frame period of the video signal is reduced to about one tenth of its standard value. The fast picture can accordingly be driven by even the fastest eye movements, and it can be displayed as a stabilized image, or, more generally, in the altered retinal feedback condition. Moreover, as compared with a standard video picture, the fast image can be “flashed” over much shorter time periods. Since a standard input video signal is used for both standard and fast video pictures, all the image processing facilities of commercial videographic systems can be fully exploited by the proposed device.     

Visual influences on auditory pluck and bow judgments

In the McGurk effect, visual information specifying a speaker’s articulatory movements can influence auditory judgments of speech. In the present study, we attempted to find an analogue of the McGurk effect by using nonspeech stimuli—the discrepant audiovisual tokens of plucks and bows on a cello. The results of an initial experiment revealed that subjects’ auditory judgments were influenced significantly by the visual pluck and bow stimuli. However, a second experiment in which speech syllables were used demonstrated that the visual influence on consonants was significantly greater than the visual influence observed for pluck-bow stimuli. This result could be interpreted to suggest that the nonspeech visual influence was not a true McGurk effect. In a third experiment, visual stimuli consisting of the wordspluck andbow were found to have no influence over auditory pluck and bow judgments. This result could suggest that the nonspeech effects found in Experiment 1 were based on the audio and visual information’s having an ostensive lawful relation to the specified event. These results are discussed in terms of motor-theory, ecological, and FLMP approaches to speech perception.     

Stereo-motion cooperation and the use ofmotion disparity in the visual perception of 3-D structure

When an observer views a moving scene binocularly, both motion parallax and binocular disparity provide depth information. In Experiments lA-1C, we measured sensitivity to surface curvature when these depth cues were available either individually or simultaneously. When the depth cues yielded comparable sensitivity to surface curvature, we found that curvature detection was easier with the cues present simultaneously, rather than individually. For 2 of the 6 subjects, this effect was stronger when the component of frontal translation of the surface was vertical, rather than horizontal. No such anisotropy was found for the 4 other subjects. If a moving object is observed binocularly, the patterns of optic flow are different on the left and right retinae. We have suggested elsewhere (Cornilleau-Pérès & Droulez, in press) that this motion disparity might be used as avisual cue for the perception of a 3-D structure. Our model consisted in deriving binocular disparity from the left and right distributions of vertical velocities, rather than from luminous intensities, as has been done in classical studies on stereoscopic vision. The model led to some predictions concerning the detection of surface curvature from motion disparity in the presence or absence of intensity-based disparity (classically termedbinocular disparity). In a second set of experiments, we attempted to test these predictions, and we failed to validate our theoretical scheme from a physiological point of view.     

Illusory conjunctions and the cerebral hemispheres

Two visual half-field experiments tested Moscovitch’s (1979) proposition that cerebral asymmetry does not concern the earliest perceptual stages but only later processing. Subjects were briefly shown displays that included one (Experiment 1) or two (Experiment 2) types of forms differing in size and which, according to previous evidence, might lead to opposite laterality effects. Laterality effects were assessed for correct detections and for illusory conjunctions, both in terms of raw detection scores and in terms of perceptual discriminability (dr scores). In Experiment 1, displays included either rectangles or triangles. In the first case, the target was a cross; in the second case, it was a Star of David. A hemifield x size interaction was observed both on correct detections and on associated discriminability. Yet, no such interaction was obtained for illusory conjunctions or for associated d’ scores. In Experiment 2, the two types of forms were presented simultaneously, with the small ones either inside or outside the large ones. No laterality effects were observed. Some implications of these data for both hemispheric asymmetry and feature integration issues are discussed. The results suggest that early preattentive processes of feature extraction are not lateralized, whereas some integrative mechanisms, such as Treisman’s (1988) focal attention, may operate differently in the two hemispheres.     

Mental image reversal and verbal recoding: When ducks become rabbits

A recent debate has concerned whether classical bistable configurations (e.g., duck/rabbit) can be reinterpreted using mental imagery. Research in this field indicates that image reversal is possible only when subjects change their specification of orientation. In a series of four experiments, we demonstrate that mental reversal of classical bistable configurations( CBCs) is impeded by verbally recoding the visual pattern at the time of input. When subjects were prevented from verbally recoding visual stimuli in short-term memory, they fared systematically better in mentally reversing the CBC, even when they received no instructions to change their reference frame or specification of orientation. On this basis, we suggest a model of image reversal that takes into account the interaction between memory codes and provides a new perspective on verbal recoding, verbal overshadowing, and mental discoveries.     

Search behaviour of cats (Felis catus) in an invisible displacement test: cognition and experience

An invisible displacement test was administered to cats in order to test the hypothesis that search behaviour in this species is influenced by their limited capacity for object permanence as well as by their previous experience with the environment. Experiment 1 compared three groups of cats in a five-choice hiding task in which the hiding places could be discriminated by their spatial positions. Two groups received a visible displacement training before the invisible displacement test and one group did not. Experiment 2 compared two groups of trained subjects in the same task, but the hiding places could be discriminated by spatial and visual cues. The results confirmed that cats are unable to solve problems with invisible displacements. The visible displacement training improved their performance, but was not sufficient to make them succeed. Experience with the hiding potential of the covers also gives more persistence to search behaviour. Finally, the distribution of search attempts is not determined by the proximity to the target and is influenced only partially by the subjects' previous experience. Like Stage 5 infants, cats rely mainly on their immediate perception. They search for an object in the last location they have seen it disappear or under the nearest cover from this location.     

Changes in information as a function of a culturally appropriate smoking cessation community intervention for Hispanics

Tested a 7-month, media-based, community intervention among Hispanics in San Francisco designed to change levels of information on the damaging effects of cigarette smoking and on the availability of culturally appropriate cessation services. Three community-wide surveys of Hispanics were conducted with independent random samples, two as baselines (n = 1,660 and 2,053) and one postintervention (n = 1,965). Results showed that changes in the level of awareness of cessation services had taken place after implementation of the intervention. Furthermore, those changes took place primarily among the less acculturated Spanish-speaking Hispanics who were the target of the intervention. The changes in information reported here demonstrate that a culturally appropriate information dissemination campaign that utilizes multiple channels can produce changes in a community's level of information even when the campaign is implemented for a relatively short period.     

Tracks and affordances: The sources of a physical ontology

How is meaning assigned to those terms in a theory which are remote from direct observational instantiation? Models and analogies play a role, but close examination of theories in high energy physics shows that the design of experimental apparatus also influences the interpretation of such terms. Certain apparatus favours certain kinds of effects, and this affects the way mathematical theories are interpreted. In particular track producing apparatus becomes involved with theories in which photonic terms are picked out in the theory. A further conceptual constraint is thus introduced. It is argued that this situation favours the interpretation of dispositional properties as affordances rather than as simple dispositions.     

The role accorded to the public by philosophers of science 1

The role accorded to the public by scientists and philosophers of science has undergone an essential historical change in the last three centuries. Public participation in (witnessing of) scientific experiments was considered an important requirement for 17th century experimenters (e.g. for Boyle or Pascal). The cognitive role played by lay persons was later substantially downgraded; witnessing went out of fashion, while science became more and more esoteric and a matter for experts only. Part of this process was that all scientific disciplines became intensively compartmentalized and in consequence a rather puzzling or even paradoxical situation appeared: that the scientists themselves were and are being reduced epistemically to the status of lay persons, outside of their proper field of expertise (as was pointed out by J. Hardwig). The paper deals with some cognitive aspects of this historical process.