Space perception and William James's metaphysical presuppositions

William James's overtly philosophical work may be more continuous with his psychological work than is sometimes thought. His Essays in Radical Empiricism can be understood as an explicit statement of the absolute presupposition that formed the basis of Jamesian psychology: that direct experience is primary and has to be taken at face value. An examination of James's theory of space perception suggests that, even in his early work, he presupposed the primacy of direct experience, and that later changes in his account of space perception can be understood as making his view more consistent with this presupposition. In his earlier view of space perception, James argued that sensations were directly experienced as spatial, though he accepted that spatial relations between sensations may be constructed by higher order thought. In his later view, however, James argued that spatial relations were just as directly experienced as sensations. The work of T. H. Green may have prompted James to recognize the full consequence of his ideas and to realize that taking experience at face value required that spatial relations be thought of as intrinsic to experience rather than the result of intellectual construction.     

The Limits of Experience and Explanation: F. A. Lange and Ernst Mach on Things in Themselves

In the middle of the nineteenth century, advances in experimental psychology and the physiology of the sense organs inspired so-called ‘Back to Kant’ Neo-Kantians to articulate robustly psychologistic visions of Kantian epistemology. But their accounts of the thing in itself were fraught with deep tension: they wanted to conceive of things in themselves as the causes of our sensations, while their own accounts of causal inference ruled that claim out. This paper diagnoses the source of that problem in views of one Neo-Kantan, F. A. Lange, and argues that it is solved only by Ernst Mach. No less than Lange and other Neo-Kantians, Mach was inspired to develop a psychologistic account of the foundations of knowledge, but his account also includes a coherent denial of things in themselves’ existence. Finally, this paper uses this account of Lange and Mach on things in themselves to illuminate Mach's relation to a certain strain of the Neo-Kantian philosophy of his own time: his views constitute a more fully coherent version of the psychologistic theory of knowledge Back to Kant figures tried to articulate.     

Stereomotion speed perception is contrast dependent

The effect of contrast on the perception of stimulus speed for stereomotion and monocular lateral motion was investigated for successive matches in random-dot stimuli. The familiar 'Thompson effect'--that a reduction in contrast leads to a reduction in perceived speed--was found in similar proportions for both binocular images moving in depth, and for monocular images translating laterally. This result is consistent with the idea that the monocular motion system has a significant input to the stereomotion system, and dominates the speed percept for approaching motion.     

Monocular motion adaptation affects the perceived trajectory of stereomotion

Perceived stereomotion trajectory was measured before and after adaptation to lateral motion in the dominant or nondominant eye to assess the relative contributions of 2 cues: changing disparity and interocular velocity difference. Perceived speed for monocular lateral motion and perceived binocular visual direction (BVD) was also assessed. Unlike stereomotion trajectory perception, the BVD of static targets showed an ocular dominance bias, even without adaptation. Adaptation caused equivalent biases in perceived trajectory and monocular motion speed, without significantly affecting perceived BVD. Predictions from monocular motion data closely match trajectory perception data, unlike those from BVD sources. The results suggest that the interocular velocity differences make a significant contribution to stereomotion trajectory perception.     

Introduction: A Cognitive Science Slam in Honor of Guy Van Orden

Illusory depth perception experienced in driving simulators is afforded by monocular depth information contained in visual displays. Presumably binocular convergence and binocular disparity, though useful for depth perception in real environments, may poorly contribute to illusory depth in a driving simulator. Instead, they may generate conflicting information by revealing the distance of the display screen and its flatness. Nevertheless, illusory depth induced by monocular information contained in visual displays usually produces enough immersion and realism to create the illusion of driving in a real environment.

Many authors have noted improved depth perception in paintings, photographs, and even in drawings when viewed monocularly. However, this effect, known as monocular advantage, has never been explored in driving simulation. The purpose of this experiment was to assess whether the effect might exist in driving simulation. It was expected that drivers would perceive distances in depth better and more accurately with a monocular than with a binocular viewing of the display. Distance estimates were evaluated for two types of driving maneuvers referred to as alignment and bisection. Results showed that when significant performance differences between monocular and binocular viewing conditions occurred, target cars were perceived farther in depth and more accurately using monocular vision.

Alternative viewing conditions using both eyes are discussed at the end of the article.     

Temporal properties of disparity processing revealed by dynamic random-dot stereograms

In studies of the temporal flexibility of the stereoscopic system, it has been suggested that two different processes of binocular depth perception could be responsible for the flexibility: tolerance for interocular delays and temporal integration of correlation. None has investigated the relationship between tolerance for delays and temporal integration mechanisms and none has revealed which mechanism is responsible for depth perception in dynamic random-dot stereograms. We address these questions in the present study. Across five experiments, we investigated the temporal properties of stereopsis by varying interocular correlation as a function of time in controlled ways. We presented different types of dynamic random-dot stereograms, each consisting of two pairs of alternating random-dot patterns. Our experimental results demonstrate that (i) disparities from simultaneous monocular inputs dominate those from interocular delayed inputs; (ii) stereopsis is limited by temporal properties of monocular luminance mechanisms; and (iii) depth perception in dynamic random-dot stereograms results from cross-correlation-like operation on two simultaneous monocular inputs that represent the retinal images after having been subjected to a process of monocular temporal integration of luminance.     

Monocular discs in the occlusion zones of binocular surfaces do not have quantitative depth--a comparison with Panum's limiting case

Da Vinci stereopsis is defined as apparent depth seen in a monocular object laterally adjacent to a binocular surface in a position consistent with its occlusion by the other eye. It is widely regarded as a new form of quantitative stereopsis because the depth seen is quantitatively related to the lateral separation of the monocular element and the binocular surface (Nakayama and Shimojo 1990 Vision Research 30 1811-1825). This can be predicted on the basis that the more separated the monocular element is from the surface the greater its minimum depth behind the surface would have to be to account for its monocular occlusion. Supporting evidence, however, has used narrow bars as the monocular elements, raising the possibility that quantitative depth as a function of separation could be attributable to Panum's limiting case (double fusion) rather than to a new form of stereopsis. We compared the depth performance of monocular objects fusible with the edge of the surface in the contralateral eye (lines) and non-fusible objects (disks) and found that, although the fusible objects showed highly quantitative depth, the disks did not, appearing behind the surface to the same degree at all separations from it. These findings indicate that, although there is a crude sense of depth for discrete monocular objects placed in a valid position for uniocular occlusion, depth is not quantitative. They also indicate that Panum's limiting case is not, as has sometimes been claimed, itself a case of da Vinci stereopsis since fusibility is a critical factor for seeing quantitative depth in discrete monocular objects relative to a binocular surface.     

Reid's Foundation for the Primary/Secondary Quality Distinction

Reid offers an under-appreciated account of the primary/secondary quality distinction. He gives sound reasons for rejecting the views of Locke, Boyle, Galileo and others, and presents a better alternative, according to which the distinction is epistemic rather than metaphysical. Primary qualities, for Reid, are qualities whose intrinsic natures can be known through sensation. Secondary qualities, on the other hand, are unknown causes of sensations. Some may object that Reid's view is internally inconsistent, or unacceptably relativistic. However, a deeper understanding shows that it is consistent, and relative only to normal humans. To acquire this deeper understanding, one must also explore the nature of dispositions, Reid's rejection of the theory of ideas, his distinction between sensation and perception, and his distinction between natural and acquired perceptions.     

Convergence as a cue to depth

A test that presents conflicting monocular and vergence cues to depth shows that approximately two-thirds of the population can use convergence as a cue to depth. The remaining one-third apparently cannot use this cue. These differences in the role of convergence in depth perception reflect individual differences in the neural mechanisms underlying depth perception.     

A comparison of monocular and binocular depth perception in 5- and 7-month-old infants

Monocular depth perception was compared with binocular depth perception in 5- and 7-month-old infants. Reaching was used as the dependent measure. Two objects, identical except in size, were presented simultaneously to each infant. The smaller object was within reach for the infants while the larger object was just beyond reach. The two objects subtended equal visual angles from the infants' observation point. With binocular presentation, 96% of the 7-month-olds' reaches and 89% of the 5-month-olds' reaches were for the nearer object. With monocular presentation, 58% of the 7-month-olds' reaches and 65% of the 5-month-olds' reaches were for the nearer object. The reaching preferences observed in the monocular condition indicated sensitivity to monocular depth information (motion parallax, accommodation, and relative size information were available). Binocular viewing, however, resulted in a far more consistent tendency to reach for the nearer object. This result suggests that the infants' perception of the objects' distances was more veridical in the binocular condition than in the monocular condition.     

The contribution of monocular depth cues to scene perception by pigeons

The contributions of different monocular depth cues to performance of a scene perception task were investigated in 4 pigeons. They discriminated the sequential depth ordering of three geometric objects in computer-rendered scenes. The orderings of these objects were specified by the combined presence or absence of the pictorial cues of relative density, occlusion, and relative size. In Phase 1, the pigeons learned the task as a direct function of the number of cues present. The three monocular cues contributed equally to the discrimination. Phase 2 established that differential shading on the objects provided an additional discriminative cue. These results suggest that the pigeon visual system is sensitive to many of the same monocular depth cues that are known to be used by humans. The theoretical implications for a comparative psychology of picture processing are considered.     

Perceiving the intensity of light

The relationship between luminance (i.e., the photometric intensity of light) and its perception (i.e., sensations of lightness or brightness) has long been a puzzle. In addition to the mystery of why these perceptual qualities do not scale with luminance in any simple way, "illusions" such as simultaneous brightness contrast, Mach bands, Craik-O'Brien-Cornsweet edge effects, and the Chubb-Sperling-Solomon illusion have all generated much interest but no generally accepted explanation. The authors review evidence that the full range of this perceptual phenomenology can be rationalized in terms of an empirical theory of vision. The implication of these observations is that perceptions of lightness and brightness are generated according to the probability distributions of the possible sources of luminance values in stimuli that are inevitably ambiguous.     

Infants' distance perception from linear perspective and texture gradients

This study investigated 5- and 7-month-old infants' abilities to perceive objects' distances from pictorial depth cues, the depth cues available to a stationary, monocular viewer. Infants viewed a display in which texture gradients and linear perspective, two pictorial depth cues, created an illusion of two objects resting at different distances on a textured surface. Under monocular viewing conditions, 7-month-olds reached preferentially for the apparently nearer object, indicating that they perceived the objects' relative distances specified by pictorial depth cues. Under binocular viewing conditions, these infants showed no reaching preference. This finding rules out interpretations of the results not based on the objects' perceived distances. The 5-month-olds' reaching preferences were not significantly different in the experimental (monocular) and control (binocular) conditions. These infants, therefore, did not show clear evidence of distance perception from pictorial depth cues.     

Infants’ sensitivity to the depth cue of shading

Five- and 7-month-old infants were tested for sensitivity to the depth cue of shading. Infants were presented with two displays: a surface in which a convexity and a concavity were molded and a photograph in which shading specified a convexity and a concavity. Each display was presented under both monocular and binocular viewing conditions. Reaching was observed as the dependent measure. Infants in both age groups reached preferentially for the actual convexity in both the monocular and binocular viewing conditions. In the monocular photograph condition, the 7-month-olds reached preferentially for the apparent convexity specified by shading, indicating that they perceived it to be an actual convexity. These infants showed no significant reaching preference in the binocular photograph condition. This finding rules out interpretations of the infants’ reaching not based on perceived depth. The results therefore suggest that the 7-month-olds perceived depth from shading. The 5-month-olds showed no significant reaching preferences when viewing the photograph; thus, they showed no evidence of depth perception from shading. These findings are consistent with the results of a number of studies that have investigated infants’ sensitivity to pictorial depth cues. Together, these studies suggest that the ability to perceive depth from pictorial cues may first develop between 5 and 7 months of age.     

The Philosophical Roots of Ernst Mach's Economy of Thought

A full appreciation for Ernst Mach's doctrine of the economy of thought must takeaccount of his direct realism about particulars (elements) and his anti-realism aboutspace-time laws as economical constructions. After a review of thought economy,its critics and some contemporary forms, the paper turns to the philosophical rootsof Mach's doctrine. Mach claimed that the simplest, most parsimonious theorieseconomized memory and effort by using abstract concepts and laws instead ofattending to the details of each individual event or experiment. For Mach, theindividual case never truly repeated in all of its uniqueness, nor was all of theindividual detail of a physical element adequately captured in abstract laws andschemata, however necessary these were for the pursuit of science. As can beshown from specific passages, some already published, some not, Mach's elementsincluded physical qualia in nature similar to Russell's unsensed sensibilia, whichexisted even where there were no conscious observers. An argument will be presentedto make the case that Mach believed in the mind-independent elements from the 1870son, while other aspects of his thought evolved over time; I have thus dated the referencesto reflect this historical progression. I concentrate on Mach's ontology, as it bears oneconomy of thought, not his epistemology per se, which might well have been restrictedto observable elements/ sensations. After his own conversion to neutral monism, in the1920s, Bertrand Russell echoed Mach's call for a `future science' capable of handlingthe `intrinsic character' of qualitative data directly without the excessive abstraction ofphysics.     

Is the anisotropy of perceived 3-D shape invariant across scale?

A number of studies have resulted in the finding of a 3-D perceptual anisotropy, whereby spatial intervals oriented in depth are perceived to be smaller than physically equal intervals in the frontoparallel plane. In this experiment, we examined whether this anisotropy is scale invariant. The stimuli were L shapes created by two rods placed flat on a level grassy field, with one rod defining a frontoparallel interval, and the other, a depth interval. Observers monocularly and binocularly viewed L shapes at two scales such that they were projectively equivalent under monocular viewing. Observers judged the aspect ratio (depth/width) of each shape. Judged aspect ratio indicated a perceptual anisotropy that was invariant with scale for monocular viewing, but not for binocular viewing. When perspective is kept constant, monocular viewing results in perceptual anisotropy that is invariant across these two scales and presumably across still larger scales. This scale invariance indicates that the perception of shape under these conditions is determined independently of the perception of size.     

Binocular vision and spatial perception in 4- and 5-month-old infants

Four experiments investigated the relation between the development of binocular vision and infant spatial perception. Experiments 1 and 2 compared monocular and binocular depth perception in 4- and 5-month-old infants. Infants in both age groups reached more consistently for the nearer of two objects under binocular viewing conditions than under monocular viewing conditions. Experiments 3 and 4 investigated whether the superiority of binocular depth perception in 4-month-olds is related to the development of sensitivity to binocular disparity. Under binocular viewing conditions in Experiment 3, infants identified as disparity-sensitive reached more consistently for the nearer object than did infants identified as disparity-insensitive. The two groups' performances did not differ under monocular viewing conditions. These results suggest that, binocularly, the disparity-sensitive infants perceived the objects' distances more accurately than did the disparity-insensitive infants. In Experiment 4, infants were habituated to an object, then presented with the same object and a novel object that differed only in size. Disparity-sensitive infants showed size constancy by recovering from habituation when viewing the novel object. Disparity-insensitive infants did not show clear evidence of size constancy. These findings suggest that the development of sensitivity to binocular disparity is accompanied by a substantial increase in the accuracy of infant spatial perception.     

Binocular rivalry and stereoscopic depth perception

An investigation was made of stimulus factors causing retinal rivalry or allowing stereoscopic depth perception, given a requisite positional disparity. It is shown that similar colour information can be “filtered” out from both eyes; that stereopsis is not incompatible with rivalry and suppression of one aspect of the stimulus, and that the strongest cue for perception of stereoscopic depth is intensity difference at the boundaries of the figures in the same direction at each eye. Identity of colour can also act as a cue for stereopsis. The brightness of different monocular figures seen in the stereoscope in different combinations was estimated by a matching technique, and it is suggested that the perceived brightness is a compromise between the monocular brightness difference between figure and ground seen in relation to the binocular fused background, and the mean brightness of the figures. The results are discussed in terms of neurophysiological “on,” “off” and continuous response fibres.     

Assessment of depth perception in cats

A behavioural method is described for the assessment of depth perception of kittens. Measurement is made of the smallest separation in depth that can be discriminated between two adjacent stimuli under both monocular and binocular viewing conditions. Normal animals can discriminate much smaller separations in depth when using two eyes than with monocular viewing, implying the presence of a cue to depth that is uniquely available with binocular viewing. The test provides a quick and reliable way of screening animals for stereopsis.