A Note on (K)Nots: Response to Robert W. Kentridge''s Commentary

GY, an extensively studied human hemianope, is aware of salient visual events in his cortically blind field but does not call this "vision." To learn whether he has low-level conscious visual sensations or whether instead he has gained conscious knowledge about, or access to, visual information that does not produce a conscious phenomenal sensation, we attempted to image process a stimulus s presented to the impaired field so that when the transformed stimulus T(s) was presented to the normal hemifield it would cause a sensation similar to that caused by s in the impaired field. While degradation of contrast, spatio-temporal filtering, contrast reversal, and addition of smear and random blobs all failed to match the response to a flashed bar s(f), moving textures of low contrast were accepted to match the response to a moving contrast-defined bar, s(m). Orientation and motion direction discrimination of the perceptually matched stimuli [s(m) and T(s(m))] was closely similar. We suggest that the existence of a satisfactory match indicates that GY has phenomenal vision.     

The reticence of visual phenomenal character: A spatial interpretation of transparency

It is often claimed that the phenomenal character of visual experience is ‘transparent’ in that the phenomenal features of visual experience do not seem ‘mental’. It is then claimed that this transparency speaks in favour of some theories of experience while speaking against others. In this paper, I advance both a negative and a positive thesis about transparency. My negative thesis is that visual phenomenal character is reticent in that it does not reveal whether it is mental or non-mental in nature. This, in turn, means that, by itself, transparency does not speak in favour of (and against) the theories it is often thought to speak in favour of (and against). My positive thesis is that the phenomenon referred to as the ‘transparency’ of visual phenomenal character is best characterized in spatial, not mental, terms.     

Low-Level Phenomenal Vision Despite Unilateral Destruction of Primary Visual Cortex

GY, an extensively studied human hemianope, is aware of salient visual events in his cortically blind field but does not call this “vision.” To learn whether he has low-level conscious visual sensations or whether instead he has gained conscious knowledge about, or access to, visual information that does not produce a conscious phenomenal sensation, we attempted to image process a stimulus s presented to the impaired field so that when the transformed stimulus T(s) was presented to the normal hemifield it would cause a sensation similar to that caused by s in the impaired field. While degradation of contrast, spatio-temporal filtering, contrast reversal, and addition of smear and random blobs all failed to match the response to a flashed bar s_f, moving textures of low contrast were accepted to match the response to a moving contrast-defined bar, s_m. Orientation and motion direction discrimination of the perceptually matched stimuli [s_m and T(s_m)] was closely similar. We suggest that the existence of a satisfactory match indicates that GY has phenomenal vision.     

“Seeing” shapes that are almost totally occluded: A new look at Parks’s camel

When a shape moves behind a very narrow window, or “slit,” the entire shape can be recognized, although at any instant only meaningless fragments are visible. In some manner, the human visual system has the ability to piece together these sequential fragments into a coherent shape that is seen as moving across the largely occluded field. As a first step toward understanding how this feat may be accomplished, we show some minimal conditions for recovering the direction and speed of motion of an unknown shape moving behind a slit. Two important conditions are that the object be rigid and that its motion be a simple transition in the image plane.     

The lost direction in binocular vision: the neglected signs posted by Wells, Towne, and LeConte

Studies of vision have informed theories first in philosophy and then in psychology. Over the centuries, an increasing number of phenomena have been enlisted to refute or reinforce particular theories. Nowhere has this been more evident than in binocular vision. How we see a single world with two eyes is one of the oldest and most consistently studied topics in vision research. It has been discussed at least since the time of Aristotle and it has been examined experimentally since the second century, when Ptolemy defined lines of visual correspondence for the two eyes. Prior to Wheatstone's invention of the stereoscope in the 1830s, binocular vision had been studied in terms of visual directions. The stereoscope established distance (or depth) as well as direction as dimensions of binocular vision. Subsequently, depth rather than direction has been the principal concern of students of vision, and texts in English devoted to analyses of direction rather than depth have been neglected. We examine the experiments on binocular visual direction conducted by Wells before Wheatstone, and by Towne and LeConte after him, and discuss the reasons for their neglect.     

Phenomenal identity and form perception in an infant

Gestalt psychologists described in some detail the stimulus conditions which determine which parts of an array will be seen as units possessing “phenomenal identity.” These same stimulus conditions, often called the Gestalt laws, were held to be effective determinants of form perception too. A previous study indicated that only one of the Gestalt laws, common fate, was an effective determinant of phenomenal identity in human infants of less than 16 weeks of age. The present study using a more powerful technique shows that another of the Gestalt laws, good continuation, is an effective determinant of phenomenal identity and form perception in infants of 36 days of age. A third variable, proximity, is not effective in this age range.     

BLURRED VISION AND THE TRANSPARENCY OF EXPERIENCE

Abstract:  This paper considers an objection to intentionalism (the view that the phenomenal character of experience supervenes on intentional content) based on the phenomenology of blurred vision. Several intentionalists, including Michael Tye, Fred Dretske, and Timothy Crane, have proposed intentionalist explanations of blurred vision phenomenology. I argue that their proposals fail and propose a solution of my own that, I contend, is the only promising explanation consistent with intentionalism. The solution, however, comes at a cost for intentionalists; it involves rejecting the "transparency of experience", a doctrine that has been the basis for the central argument in favor of intentionalism.     

人眼深度运动知觉的研究

人类的深度运动知觉,是通过检测二维平面内的相对运动而形成的。本文在心理物理学实验基础上,揭示该机制的数学与生理学实现形式。视觉系统中存在对视平面内的相对运动敏感的神经元,构成深度运动的检测机制,产生单眼深度运动知觉与双眼深度运动知觉。在心理学上,视觉利用物体视角变化及大小知觉的恒常性判断深度运动。文中还初步讨论了人类的深度运动知觉与蜜蜂,家蝇等昆虫的深度运动知觉的区别。     

Are there unconscious perceptual processes?

Blindsight and vision for action seem to be exemplars of unconscious visual processes. However, researchers have recently argued that blindsight is not really a kind of unconscious vision but is rather severely degraded conscious vision. Morten Overgaard and colleagues have recently developed new methods for measuring the visibility of visual stimuli. Studies using these methods show that reported clarity of visual stimuli correlates with accuracy in both normal individuals and blindsight patients. Vision for action has also come under scrutiny. Recent findings seem to show that information processed by the dorsal stream for online action contributes to visual awareness. Some interpret these results as showing that some dorsal stream processes are conscious visual processes (e.g., Gallese, 2007; Jacob & Jeannerod, 2003). The aim of this paper is to provide new support for the more traditional view that blindsight and vision for action are genuinely unconscious perceptual processes. I argue that individuals with blindsight do not have access to the kind of purely qualitative color and size information which normal individuals do. So, even though people with blindsight have a kind of cognitive consciousness, visual information processing in blindsight patients is not associated with a distinctly visual phenomenology. I argue further that while dorsal stream processing seems to contribute to visual awareness, only information processed by the early dorsal stream (V1, V2, and V3) is broadcast to working memory. Information processed by later parts of the dorsal stream (the parietal lobe) never reaches working memory and hence does not correlate with phenomenal awareness. I conclude that both blindsight and vision for action are genuinely unconscious visual processes.     

Stored representations of three-dimensional objects in the absence of two-dimensional cues

Object recognition was studied in human subjects to determine whether the storage of the visual objects was in a two-dimensional or a three-dimensional representation. Novel motion-based and disparity-based stimuli were generated in which three-dimensional and two-dimensional form cues could be manipulated independently. Subjects were required to generate internal representations from motion stimuli that lacked explicit two-dimensional cues. These stored internal representations were then matched against internal three-dimensional representations constructed from disparity stimuli. These new stimuli were used to confirm prior studies that indicated the primacy of two-dimensional cues for view-based object storage. However, under tightly controlled conditions for which only three-dimensional cues were available, human subjects were also able to match an internal representation derived from motion of that of disparity. This last finding suggests that there is an internal storage of an object's representations in three dimensions, a tenet that has been rejected by view-based theories. Thus, any complete theory of object recognition that is based on primate vision must incorporate three-dimensional stored representations.     

Conscious Vision for Action Versus Unconscious Vision for Action?

David Milner and Melvyn Goodale’s dissociation hypothesis is commonly taken to state that there are two functionally specialized cortical streams of visual processing originating in striate (V1) cortex: a dorsal, action‐related “unconscious” stream and a ventral, perception‐related “conscious” stream. As Milner and Goodale acknowledge, findings from blindsight studies suggest a more sophisticated picture that replaces the distinction between unconscious vision for action and conscious vision for perception with a tripartite division between unconscious vision for action, conscious vision for perception, and unconscious vision for perception. The combination excluded by the tripartite division is the possibility of conscious vision for action. But are there good grounds for concluding that there is no conscious vision for action? There is now overwhelming evidence that illusions and perceived size can have a significant effect on action ( Bruno & Franz, 2009 ; Dassonville & Bala, 2004 ; Franz & Gegenfurtner, 2008 ; McIntosh & Lashley, 2008 ). There is also suggestive evidence that any sophisticated visual behavior requires collaboration between the two visual streams at every stage of the process ( Schenk & McIntosh, 2010 ). I nonetheless want to make a case for the tripartite division between unconscious vision for action, conscious vision for perception, and unconscious vision for perception. My aim here is not to refute the evidence showing that conscious vision can affect action but rather to argue (a) that we cannot gain cognitive access to action‐guiding dorsal stream representations, and (b) that these representations do not correlate with phenomenal consciousness. This vindicates the semi‐conservative view that the dissociation hypothesis is best understood as a tripartite division.     

Modal completion: critical variables in apparent transparency

Conditions for perceptual modal completion are investigated using a stimulation pattern consisting of a figure moving behind a black opaque strip. This configuration leads, depending on conditions, either to the amodal Michotte tunnel effect, or to modal completion, ie the apparent transparency phenomenon. Four experiments are reported in which an attempt was made to define the critical variables of this latter effect. The results show that modal completion is not typically related to luminance interactions, ie to assimilation, but depends on the figural dominance of the filled-in object, this being determined by structural factors such as figure-ground relationship and stimulation change. The effect also depends strongly on the complexity of the spatiotemporal integration needed to maintain phenomenal identity of the object. No significant effect was found for the two other variables investigated, ie formal complexity of the figure and depth between the figure and the strip. The data are discussed in relation to those on moving visual phantoms.     

A theory of phenomenal geometry and its applications

The geometry of perceived space (phenomenal geometry) is specified in terms of three basic factors: the perception of direction, the perception of distance or depth, and the perception of the observer's own position or motion. The apparent spatial locations of stimulus points resulting from these three factors thereupon determine the derived perceptions of size, orientation, shape, and motion. Phenomenal geometry is expected to apply to both veridical and illusory perceptions. It is applied here to explain a number of representative illusions, including the illusory rotation of an inverted mask (Gregory, 1970), a trapezoidal window (Ames, 1952), and any single or multiple point stimuli in which errors in one or more of the three basic factors are present. It is concluded from phenomenal geometry that the size-distance and motion-distance invariance hypotheses are special cases of the head motion paradigm, and that proposed explanations in terms of compensation, expectation, or logical processes often are unnecessary for predicting responses to single or multiple stimuli involving head or stimulus motion. Two hypotheses are identified in applying phenomenal geometry. It is assumed that the perceptual localization of stimulus points determines the same derived perceptions, regardless of the source of perceptual information supporting the localizations. This assumption of cue equivalence or cue substitution provides considerable parsimony to the geometry. Also, it is assumed that the perceptions specified by the geometry are internally consistent. Departures from this internal consistency, such as those which occur in the size-distance paradox, are considered to often reflect the intrusion of nonperceptual (cognitive) processes into the responses. Some theoretical implications of this analysis of phenomenal geometry are discussed.     

Phenomenology and Perceptual Content

Terence Horgan and John Tienson argue that there is phenomenal intentionality, that is, “a kind of intentionality, pervasive in human mental life, that is constitutively determined by phenomenology alone”. However, their arguments are open to two lines of objection. First, Horgan and Tienson are not sufficiently clear as to what kind of content it is that they take to be determined by, or to supervene on, phenomenal character. Second, critics have objected that, for their conclusion to follow, Horgan and Tienson would first have to establish the covariation of phenomenology and intentional content, but even so, phenomenal intentionality would still emerge as less plausible than its converse, representationalism. I will address these two challenges by appeal to Husserlian ideas. A consideration of perceptual phenomenology (i.e., phenomenal character) shows that there is a kind of perceptual content that is, indeed, determined by phenomenal character. Such content is conceived in terms of fulfillment conditions, or what it takes to bring aspects of objects and scenes to different, and more complete, ways of givenness. We can establish the primacy of phenomenology, relative to such fulfillment‐conditional content, by tracing it back to the basic phenomenology of visual and other sensations.     

The aesthetic appeal of auditory-visual synaesthetic perceptions in people without synaesthesia

The term 'visual music' refers to works of art in which both hearing and vision are directly or indirectly stimulated. Our ability to create, perceive, and appreciate visual music is hypothesised to rely on the same multisensory processes that support auditory visual (AV) integration in other contexts. Whilst these mechanisms have been extensively studied, there has been little research on how these processes affect aesthetic judgments (of liking or preference). Studies of synaesthesia in which sound evokes vision and studies of cross-modal biases in non-synaesthetes have revealed non-arbitrary mappings between visual and auditory properties (eg high-pitch sounds being smaller and brighter). In three experiments, we presented members of the general population with animated AV clips derived from synaesthetic experiences and contrasted them with a number of control conditions. The control conditions consisted of the same clips rotated or with the colour changed, random AV pairings, or animated clips generated by non-synaesthetes. Synaesthetic AV animations were generally preferred over the control conditions. The results suggest that non-arbitrary AV mappings, present in the experiences of synaesthetes, can be readily appreciated by others and may underpin our tendency to engage with certain forms of art.     

Visual discrimination of local surface depth and orientation

Many theoretical analyses of 3-dimensional form perception assume that visible surfaces in the environment are perceptually represented in terms of local mappings of metric depth and/or orientation. Although this approach is often taken for granted in the study of human vision, there have been relatively few attempts to demonstrate its psychological validity empirically. In an effort to shed new light on this issue, our research has been designed to investigate the accuracy with which observers can discriminate metric depth and orientation intervals on smoothly curved surfaces. Observers were presented with visual images of surfaces defined by shading and/or texture, on which two pairs of points were designated with small dots. In Experiment 1, their task was to identify which pair of points had a greater difference in depth; in Experiment 2 they were required to judge which pair had a greater difference in orientation. The Weber fractions obtained for these tasks were 10 to 100 times greater than those that have been reported for other types of sensory discrimination, indicating that the perception of metric structure from these displays is surprisingly coarse grained.     

Measures of perceived linear size, sagittal motion, and visual angle from optical expansions and contractions

Using monocular observation, open-loop measurements were obtained of the perceptions of linear size, angular size, and sagittal motion associated with the terminal (largest or smallest) stimuli of repetitive optical expansions and contractions using 1-D or 2-D displays produced on a video monitor at a constant distance from the observer. The perceptions from these dynamic conditions were compared with those from static conditions in which the stimuli were of the same physical size and at the same physical distance as the terminal dynamic stimuli, but that were not part of the optical expansions or contractions. One result, as expected, was that the measures of perceived linear and angular size differed, but also, unexpectedly, some substantial errors were associated with the measures of perceived angular size. Another result was that the amount of size constancy was considerably less than was expected from the obtained amount of perceived motion in depth. Consistent with the latter result, it was found that the size-distance invariance hypothesis (SDIH), using the physical visual angles of the terminal stimuli, predicted only about half of the perceived motion in depth obtained with the dynamic changes. Using the obtained measures of perceived visual angles in the SDIH increased rather than decreased the error in predicting the amount of motion in depth as perceived. An additional experiment suggests that at least some of the error in the measurement of the perceived visual angle is a consequence of error in the perceived origin of the visual angles. The absence of the expected relation between size constancy and perceived motion in depth in the dynamic conditions is hypothesized to be due to cognitive processes associated with off-sized perceptions of the stimuli.     

How is motion disparity integrated with binocular disparity in depth perception?

Two experiments presented motion disparity conflicting with binocular disparity to examine how these cues determined apparent depth order (convex, concave) and depth magnitude. In each experiment, 8 subjects estimated the depth order and depth magnitude. The first experiment showed the following. (1) The visual system used one of these cues exclusively in selecting a depth order for each display. (2) The visual system integrated the depth magnitude information from these cues by a weighted additive fashion if it selected the binocular disparity in depth order perception and if the depth magnitude specified by motion disparity was small relative to that specified by binocular disparity. (3) The visual system ignored the depth magnitude information of binocular disparity if it selected the motion disparity in depth order perception. The second experiment showed that these three points were consistent whether the subject’s head movement or object movement generated motion disparity.