Four-month-old infants were allowed to manipulate, without vision, two rings attached to a bar that permitted each ring to undergo rotary motion against a fixed surface. In different conditions, the relative motions of the rings were rigid, independent, or opposite, and they circled either the same fixed point outside the zone of manipulation or spatially separated points. Infants’ perception of the ring assemblies were affected by the nature of the rotary motion in two ways. First, infants (...) perceived a unitary object when the felt ends of the object underwent a common, rigid rotary motion; perception of object unity was stronger in this condition than when the ends underwent either independent or opposite rotary motions. Second, infants perceived two distinct objects when the felt ends of the objects underwent independent rotary motions that centred on distinct fixed points. Perception of the distinctness of the objects was less clear when the ends underwent opposite or independent rotary motions that centred on a common fixed point. These findings provide the first evidence that infants are sensitive to rotary motion patterns and can extrapolate a global pattern of rigid motion from the distinct, local velocities that they produce and experience at their two hands. (shrink)

This paper defends a 'punctivist' conception of consciousness from recent attacks by Ian Phillips and Matthew Soteriou. As we intend it, 'punctivism' is the view that a subject's experience over some interval is determined by their experiential states at each instant during it. Phillips and Soteriou both offer ingenious arguments purporting to show that the punctivist is unable to make sense of motion perception; and that only by adopting an 'holistic' conception -- whereby a subject's instantaneous experiences are (...) determined by their experience over the interval -- can we make sense of the puzzles such phenomena pose. We contend that both arguments invoke dubious claims, their proffered solutions come with highly controversial commitments, and, if we take punctivism seriously, it is difficult to see why the so-called puzzles should be puzzling in the first place. A punctivist model of motion perception is proposed in response, and objections anticipated. (shrink)

According to the traditional inferential theory of perception, percepts of object motion or stationarity stem from an evaluation of afferent retinal signals (which encode image motion) with the help of extraretinal signals (which encode eye movements). According to direct perception theory, on the other hand, the percepts derive from retinally conveyed information only. Neither view is compatible with a perceptual phenomenon that occurs during visually induced sensations of ego motion (vection). A modified version of inferential (...) theory yields a model in which the concept of extraretinal signals is replaced by that of reference signals, which do not encode how the eyes move in their orbits but how they move in space. Hence reference signals are produced not only during eye movements but also during ego motion (i.e., in response to vestibular stimulation and to retinal image flow, which may induce vection). The present theory describes the interface between self-motion and object-motion percepts. An experimental paradigm that allows quantitative measurement of the magnitude and gain of reference signals and the size of the just noticeable difference (JND) between retinal and reference signals reveals that the distinction between direct and inferential theories largely depends on: (1) a mistaken belief that perceptual veridicality is evidence that extraretinal information is not involved, and (2) a failure to distinguish between (the perception of) absolute object motion in space and relative motion of objects with respect to each other. The model corrects these errors, and provides a new, unified framework for interpreting many phenomena in the field of motion perception. (shrink)

Self-motion through space generates a visual pattern called optic flow. It can be used to determine one’s direction of self-motion (heading). Previous studies have already shown thatthis perceptual ability, which is of critical importance during everyday life, changes with age. In most of these studies subjects were asked to judge whether they appeared to be heading to the left or right of a target. Thresholds were found to increase continuously with age. In our current study, we were interested (...) in absolute rather than relative heading judgements and in the question about a potential neural correlate of an age-related deterioration of heading perception. Two groups, older test subjects and younger controls, were shown optic flow stimuli in a virtual-reality setup. Visual stimuli simulated self-motion through a 3-D cloud of dots and subjects had to indicate their perceived heading direction after each trial. In different subsets of experiments we varied individuallyrelevant stimulus parameters: presentation time, number of dots in the display, stereoscopic vs. non-stereoscopic stimulation, and motion coherence. We found decrements in heading performance with agefor each stimulus parameter. In a final step we aimed to determine a putative neural basis of this behavioural decline. To this end we modified a neural network model which previously has proven to be capable of reproduce and predict certain aspects of heading perception. We show that the observed data can be modeled by implementing an age related neuronal cell loss in this neural network. We conclude that a continuous decline of certain aspects of motion perception, among them heading, might directly be based on anage-related progressive loss of groups of neurons being activated by visual motion. (shrink)

This paper offers an inconsistent model of motion perception. It was prompted by work on inconsistent motion due to Hegel and, following him, Priest. But the paper skirts Hegel's full scale idealism, by proposing that the inconsistency is with the cognitive contents of motion perception. The paper draws on work in the psychology of perception, and in the theory of inconsistency. I begin by noting the prima facie argument that temporal change threatens inconsistency, and (...) canvassing ways in which this might be avoided. The orthodox reply to the prima facie argument is that one and the same thing can have different incompatible properties at different times. This is plausible when applied to motion in the physical world. However, applied to cognition, it can be seen that the phenomenon of phi or beta, combined with the mechanism of a Reichardt detector, lends support to one key step in the prima facie argument, namely re-identification over time. The inconsistency of the model is then seen to follow from application of the Fade Principle. Advantages of the model are stressed: including a simple explanation of the debilitating condition of akinetopsia, that is, motion blindness; and a suggestion as to how to account for the “moving now.”. (shrink)

In line with my model of object motion perception (Wertheim 1994) and in contradistinction to what Stoffregen (1994) states, Sauvan's data suggest that percepts of motion are not sense specific. It is here argued that percepts of object- or self-motion are neither sense specific nor do they necessarily stem from what Stoffregen calls “kinematic events.” Stoffregen's error is in believing that we can only perceive object- or self-motion relative to other objects, which implies a failure (...) to realise that percepts of absolute object- or self-motion in space (relative to the earth's surface) do exist as well, even when the earth's surface itself is not perceived. (shrink)

Human infants begin very early in life to take advantage of multisensory information by extracting the invariant amodal information that is conveyed redundantly by multiple senses. Here we addressed the question as to whether infants can bind multisensory moving stimuli, and whether this occurs even if the motion produced by the stimuli is only illusory. Three- to four-month-old infants were presented with two bimodal pairings: visuo-tactile and audio-visual. Visuo-tactile pairings consisted of apparently vertically moving bars (the Barber Pole illusion) (...) moving in either the same or opposite direction with a concurrent tactile stimulus consisting of strokes given on the infant’s back. Audio-visual pairings consisted of the Barber Pole illusion in its visual and auditory version, the latter giving the impression of a continuous rising or ascending pitch. We found that infants were able to discriminate congruently (same direction) vs. incongruently moving (opposite direction) pairs irrespective of modality (Experiment 1). Importantly, we also found that congruently moving visuo-tactile and audio-visual stimuli were preferred over incongruently moving bimodal stimuli (Experiment 2). Our findings suggest that very young infants are able to extract motion as amodal component and use it to match stimuli that only apparently move in the same direction. (shrink)

A new motion illusion is discussed in relation to the idea of vision as a Grand Illusion. An experiment shows that this 'Tinkerbell effect' is a good example of a visual illusion supported by low-level stimulus information, but resulting from integration principles probably necessary for normal perception.

The concept of rigid reference frame and of constricted spatial metric, given in the previous work [Class. Quantum Grav. 21, 3067 (2004)] are here applied to some specific space-times: in particular, the rigid rotating disc with constant angular velocity in Minkowski space-time is analyzed, a new approach to the Ehrenfest paradox is given as well as a new explanation of the Sagnac effect. Finally the anisotropy of the speed of light and its measurable consequences in a reference frame (...) co-moving with the Earth are discussed. (shrink)

A mime presented on videotape Adler’s six great ideas of truth, goodness, beauty, liberty, equality, and justice; their opposites; and the transitions from the positive or “good” concepts to their opposites. Using Johansson’s (1973) technique, the performer’s 12 joints were marked with points of light. Overall, the viewers had marginal success in identifying the concepts, but females were much more successful than males in identifying the “bad” ones of evil, slavery, falsehood, and ugliness, averaging 62% correct to the males’ 23%. (...) The results agree with Hall’s (1984) discussion of sex differences in the interpretation of nonverbal behavior. (shrink)

Following lesions to the primary visual cortex, some patients maintain visual capacities within areas of the visual field in which they are defined as clinically blind by static field perimetry. Blindsight describes the ability to discriminate visual stimuli in the absence of awareness of the stimuli in such patients. Some patients exhibit blindsight, but others are aware of the stimuli with which they are presented, a response mode that has been referred to as residual vision. The two response modes are (...) of great interest as they are capable of providing us with information concerning the conscious and unconscious processing of visual signals in humans. However, determining consciousness in these patients is a difficult task and relies on the patient assessing and then reporting on his awareness. In this paper, an experiment is described which is capable of demonstrating conscious visual processing of motion under conditions where the observer is not required to assess his level of awareness. In applying this technique to a human hemianope, GY, it is demonstrated that GY has veridical and conscious perception of visual motion presented to his blind hemifield. Although previously reported, this result can be derived without any reference to GY's commentary on his blind field perception. (shrink)

Kant, Wittgenstein, and Husserl all held that visual awareness of objects requires visual awareness of the space in which the objects are located. There is a lively debate in the literature on spatial perception whether this view is undermined by the results of experiments on a Balint’s syndrome patient, known as RM. I argue that neither of two recent interpretations of these results is able to explain RM’s apparent ability to experience motion. I outline some ways in which (...) each interpretation may respond to this challenge, and suggest which way of meeting the challenge is preferable. I conclude that RM retains some awareness of the larger space surrounding the objects he sees. (shrink)

The relationship between brain activity and conscious visual experience is central to our understanding of the neural mechanisms underlying perception. Binocular rivalry, where monocular stimuli compete for perceptual dominance, has been previously used to dissociate the constant stimulus from the varying percept. We report here fMRI results from humans experiencing binocular rivalry under a dichoptic stimulation paradigm that consisted of two drifting random dot patterns with different motion coherence. Each pattern had also a different color, which both enhanced (...) rivalry and was used for reporting which of the two patterns was visible at each time. As the perception of the subjects alternated between coherent motion and motion noise, we examined the effect that these alternations had on the strength of the MR signal throughout the brain. Our results demonstrate that motion perception is able to modulate the activity of several of the visual areas which are known to be involved in motion processing. More specifically, in addition to area V5 which showed the strongest modulation, a higher activity during the perception of motion than during the perception of noise was also clearly observed in areas V3A and LOC, and less so in area V3. In previous studies, these areas had been selectively activated by motion stimuli but whether their activity reflects motion perception or not remained unclear; here we show that they are involved in motion perception as well. The present findings therefore suggest a lack of a clear distinction between ?processing? versus ?perceptual? areas in the brain, but rather that the areas involved in the processing of a specific visual attribute are also part of the neuronal network that is collectively responsible for its perceptual representation. (shrink)

Eye-related movements such as blinks and microsaccades are modulated during bistable perceptual tasks. However, if they play an active role during internal perceptual switches is not known. We conducted two experiments involving an ambiguous plaid stimulus, wherein participants were asked to continuously report their percept, which could consist of either unidirectional coherent or bidirectional component movement. Our main results show that blinks and microsaccades did not facilitate perceptual switches. On the contrary, a reduction in eye movements preceded the perceptual switch. (...) Blanks, on the other hand, thought to mimic the retinal consequences of a blink, consistently led to a switch. Through the timing of the blank-introduced perceptual change, we were able to estimate the delay between the internal switch and the response. This delay further allowed us to evaluate that the reduction in blink probability co-occurred with the internal perceptual switch. Additionally, our results indicate that distinct internal processes underlie the switch to coherent vs. component percept. Blanks exclusively facilitated a switch to the coherent percept, and only the switch to coherent percept was followed by an increase in blink rate. In a second study, we largely replicated the findings and included a microsaccade analysis. Microsaccades only showed a weak relation with perceptual switches, but their direction was correlated with the perceived motion direction. Nevertheless, our data suggests an interaction between microsaccades and blinks by showing that microsaccades were differently modulated around blinks compared with blanks. This study shows that a reduction in eye movements precedes internal perceptual switches indicating that the rate of blinks can set the stage for a reinterpretation of sensory input. While a perceptual switch based on changed sensory input usually leads to an increase in blink rate, such an increase was only present after the perceptual switch to coherent motion but absent after the switch to component percept. This provides evidence of different underlying mechanism or internal consequence of the two perceptual switches and suggests that blinks can uncover differences in internal percept-related processes that are not evident from the percept itself. (shrink)

We investigated the key anatomical structures mediating interhemispheric integration during the perception of apparent motion across the retinal midline. Previous studies of commissurotomized patients suggest that subcortical structures mediate interhemispheric transmission but the specific regions involved remain unclear. Here, we exploit interindividual variations in the propensity of normal subjects to perceive horizontal motion, in relation to vertical motion. We characterize these differences psychophysically using a Dynamic Dot Quartet (an ambiguous stimulus that induces illusory motion). We (...) then tested for correlations between a tendency to perceive horizontal motion and fractional anisotropy (FA) (from structural diffusion tensor imaging), over subjects. FA is an indirect measure of the orientation and integrity of white matter tracts. Subjects who found it easy to perceive horizontal motion showed significantly higher FA values in the pulvinar. Furthermore, fiber tracking from an independently identified (subject-specific) visual motion area converged on the pulvinar nucleus. These results suggest that the pulvinar is an anatomical hub and may play a central role in interhemispheric integration. (shrink)