Some observations on the perception of Marroquin patterns.

Demonstrations are presented to show that the perception of structure in Marroquin patterns is disrupted if the dots comprising the pattern have opposite contrast polarity, and also if the dots comprising the pattern are separated in stereoscopic depth. It is also demonstrated that the perception of structure in a Marroquin pattern is made possible if the pattern is separated in stereoscopic depth from 'noise' dots, where the pattern structure cannot be perceived in either half of the unfused stereogram. In these respects the perception of Marroquin patterns is similar to the perception of Glass patterns. These findings are thus consistent with the proposal that the perception both of Marroquin and of Glass patterns is based on the construction of virtual lines.     

Influences of the perception of self-motion on postural parameters.

We examined how spatial and temporal characteristics of the perception of self-motion, generated by constant velocity visual motion, was reflected in orientation of the head and whole body of young adults standing in a CAVE, a virtual environment that presents wide field of view stereo images with context and texture. Center of pressure responses from a force plate and perception of self-motion through orientation of a hand-held wand were recorded. The influence of the perception of self-motion on postural kinematics differed depending upon the plane and complexity of visual motion. Postural behaviors generated through the perception of self-motion appeared to contain a confluence of the cortically integrated visual and vestibular signals and of other somatosensory inputs. This would suggest that spatial representation during motion in the environment is modified by both ascending and descending controls. We infer from these data that motion of the visual surround can be used as a therapeutic tool to influence posture and spatial orientation, particularly in more visually sensitive individuals following central nervous system (CNS) impairment.     

The independence of size perception and distance perception.

Research on distance perception has focused on environmental sources of information, which have been well documented; in contrast, size perception research has focused on familiarity or has relied on distance information. An analysis of these two parallel bodies of work reveals their lack of equivalence. Furthermore, definitions of familiarity need environmental grounding, specifically concerning the amount of size variation among different tokens of an object. To demonstrate the independence of size and distance perception, subjects in two experiments were asked to estimate the sizes of common objects from memory and then to estimate both the sizes and the distances of a subset of such objects displayed in front of them. The experiments found that token variation was a critical variable in the accuracy of size estimations, whether from memory or with vision, and that distance had no impact at all on size perception. Furthermore, when distance information was good, size had no effect on distance estimation; in contrast, at far distances, the distances to token variable or unknown objects were estimated with less accuracy. The results suggest that size perception has been misconceptualized, so that the relevant research to understand its properties has not been undertaken. The size-distance invariance hypothesis was shown to be inadequate for both areas of research.     

Spatial perception in the blind.

It is often that the spatial senses (vision, hearing and the tactual senses) operate as distinct and independent modalities and, moreover, that vision is crucial to the development of spatial abilities. However, well controlled studies of blind persons with adequate experience show that they can function usefully in space. In other words, vision is not a necessary condition for spatial awareness. On the other hand, thought the blind may be equal or even superior to the sighted when performing spatial tasks within the body space, they may be deficient, either developmentally or absolutely, in tasks which involve events at a distance from the body, principally in auditory localization. One possible explanation of the differences between blind and sighted (McKinney, 1964; Attneave & Benson, 1969, Warren, 1970) is that vision is the primary spatial reference, and inputs from other modalities are fitted to a visual map. Several criticisms of this theory are adduced and an alternative theory derived from Sherrington (1947), in which all sensory inputs map on to efferent patterns, is sketched.     

The effects of complexity on the perception of vibrotactile patterns.

Vibrotactile patterns were presented to subjects' left index fingerpads using the array from the Optacon. A set of simple (one-line) patterns and a set of complex (two-line) patterns were constructed so that they were equally identifiable when presented individually. In Experiment 1, discrimination performance was lower for two-line patterns than for one-line patterns. Communality, the number of lines that two patterns share in common, appeared to be the major factor in reducing discrimination performance for two-line patterns. Experiment 2 measured the time required to identify individual patterns. There was no significant difference in identification times for one- and two-line patterns, suggesting that features within a pattern were processed simultaneously. In the presence of a temporal masking stimulus (Experiment 3), two-line patterns were more difficult to identify than one-line patterns, but reaction times were similar for the two sets of patterns. The results suggest that varying complexity affects perception of patterns at later stages of processing.     

Psychophysical features of the transition from pure heat perception to heat pain perception.

The psychophysical features of the transition from the pure heat to the heat pain range were studied in 25 healthy subjects (mean age 28.8 years). Thirty short heat stimuli from -1.6 degrees C to +1.6 degrees C relative to the pain threshold were applied to the thenar of the left hand with an apparatus containing a Peltier thermode (nine different temperatures at 0.4 degrees C intervals). The subjects rated the sensation intensity on a visual analogue scale. The resulting stimulus/sensation intensity relations could be explained equally well (same goodness of fit) by a model with a power function (PF) and by a model with two linear regression lines (TLR), one for stimulus intensities below and one for those above the pain threshold and intersecting at the pain threshold. The slopes of the TLR model were significantly larger above the pain threshold than below it. The PF model produced exponents between 1.8 and 1.9. We conclude that to describe the transition area, it is sufficient to use simple linear models for both the pure heat and the heat pain ranges.     

Determinants of the perception of sagittal motion.

This study examines the change in the perceived distance of an object in three-dimensional space when the object and/or the observer's head is moved along the line of sight (sagittal motion) as a function of the perceived absolute (egocentric) distance of the object and the perceived motion of the head. To analyze the processes involved, two situations, labeled A and B, were used in four experiments. In Situation A, the observer was stationary and the perceived motion of the object was measured as the object was moved toward and away from the observer. In Situation B, the same visual information regarding the changing perceived egocentric distance between the observer and object was provided as in Situation A, but part or all of the change in visual egocentric distance was produced by the sagittal motion of the observer's head. A comparison of the perceived motion of the object in the two situations was used to measure the compensation in the perception of the motion of the object as a result of the head motion. Compensation was often clearly incomplete, and errors were often made in the perception of the motion of the stimulus object. A theory is proposed, which identifies the relation between the changes in the perceived egocentric distance of the object and the tandem motion of the object resulting from the perceived motion of the head to be the significant factor in the perception of the sagittal motion of the stimulus object in Situation B.     

Developmental color perception.

The purpose of this research is to extend the investigation of surface color perception to several age levels. The 108-item color perception test, originally used with young children, employs six Munsell hue matrices divided into nine combinations each of low, mid, and high chroma and low, mid, and high value across two levels of hue difficulty. The pattern of error results are the same across the age groups comprising kindergartners, fifth graders, high school sophomores, nonartist adults, and professional artists: the lower the chroma and value, the higher the error rate; the higher the chroma and value, the lower the error rate. In hues, green and red are most difficult; orange and yellow are easiest. The frequency of error is linear with respect to age: the younger the group, the higher the error. The latency data differ with respect to age: adults are slowest, followed by kindergartners and fifth graders. High school sophomores are the fastest. The remaining latency results parallel the error results: the lower the chroma and value, the longer the latency and the more difficult the hue, the longer the latency. A set of surface color perception rules are generated.     

Denial of visual perception.

An adult with the diagnosis of cortical blindness, complaining of a complete visual loss of 2 years in duration, was found to have a small preserved visual field and remarkably preserved visual abilities. Although denying visual perception, he correctly named objects, colors, and famous faces, recognized facial emotions, and read various types of single words with greater than 50% accuracy when presented in the upper right visual field. Upon confrontation regarding his apparent visual abilities, the patient continued to deny visual perceptual awareness, typically stating "I feel it." CT indicated bioccipital lesions sparing the left inferior occipital area but involving the left parietal lobe. The denial of visual perception evidenced by this patient may be explained by a disconnection of parietal lobe attentional systems from visual perception. The clinical presentation is described as representing "inverse Anton's syndrome."     

On the perception of shape from shading.

The extraction of three-dimensional shape from shading is one of the most perceptually compelling, yet poorly understood, aspects of visual perception. In this paper, we report several new experiments on the manner in which the perception of shape from shading interacts with other visual processes such as perceptual grouping, preattentive search ("pop-out"), and motion perception. Our specific findings are as follows: (1) The extraction of shape from shading information incorporates at least two "assumptions" or constraints--first, that there is a single light source illuminating the whole scene, and second, that the light is shining from "above" in relation to retinal coordinates. (2) Tokens defined by shading can serve as a basis for perceptual grouping and segregation. (3) Reaction time for detecting a single convex shape does not increase with the number of items in the display. This "pop-out" effect must be based on shading rather than on differences in luminance polarity, since neither left-right differences nor step changes in luminance resulted in pop-out. (4) When the subjects were experienced, there were no search asymmetries for convex as opposed to concave tokens, but when the subjects were naive, cavities were much easier to detect than convex shapes. (5) The extraction of shape from shading can also provide an input to motion perception. And finally, (6) the assumption of "overhead illumination" that leads to perceptual grouping depends primarily on retinal rather than on "phenomenal" or gravitational coordinates. Taken collectively, these findings imply that the extraction of shape from shading is an "early" visual process that occurs prior to perceptual grouping, motion perception, and vestibular (as well as "cognitive") correction for head tilt. Hence, there may be neural elements very early in visual processing that are specialized for the extraction of shape from shading.     

Binocular depth perception in the pigeon.

By means of a discrete-trial simultaneous discrimination procedure, pigeons were trained to respond differentially to visual arrays that were identical except that one of them contained a circle displaced in depth when viewed stereoscopically. Performance was severely disrupted when one eye was occluded. The monocular deficit was peculiar to the depth task, inasmuch as no such decrement was seen on a pattern discrimination. The results imply that presence of the displaced circle was discriminated on the basis of a binocular cue. It was also found that pigeons could discriminate the direction of the displacement. Discrimination of depth was independent of the global form and still occurred when elements of the array were randomly displaced in depth. Performance was not disrupted when the absolute convergence angle of the depth stimulus was changed. The cue that consistently accounted for the behavior seen was the detection of the relative angles of convergence--that is, the retinal disparity of the two planes in depth. Thus, despite the lateral position of the eyes of the pigeon, a small binocular field mediates the binocular discrimination of near objects in depth.     

Aristotle on the perception of universals

Aristotle claims that ‘although we perceive particulars, perception is of universals; for instance of human being, not of Callias-the-human-being’ (APo II.19 100a16–b1). I offer an interpretation of this claim and examine its significance in Aristotle's epistemology.     

Effects of early common features on form perception.

Recognizing forms may involve a contingency in which later processing is modified, depending on the results of early analyses. This hypothesis can be distinguished from feature models, in which features (including early global features) accumulate over time. In four experiments, shape primes were presented briefly, followed immediately and in the same location by a similarly or differently shaped target, and then a mask. Accuracy was measured with a two-alternative forced-choice discrimination. The primes facilitated discriminations between a similarly shaped target and differently shaped foil, as would be expected. More important is that the primes also facilitated discriminations between similarly shaped targets and similarly shaped foils, even though the primes contained only features common to the alternatives and thus provided no discrimination-relevant information. The facilitation effect was constant over variations in the size of the target set, the type of mask, and the type of baseline condition. This result is consistent with the idea of early-to-late contingencies in processing but was not predicted by feature models.     

Characterizing the influence of native language experience on adult speech perception.

Previous cross-language research has indicated that some speech contrasts present greater perceptual difficulty for adult non-native listeners than others do. It has been hypothesized that phonemic, phonetic, and acoustic factors contribute to this variability. Two experiments were conducted to evaluate systematically the role of phonemic status and phonetic familiarity in the perception of non-native speech contrasts and to test predictions derived from a model proposed by Best, McRoberts, and Sithole (1988). Experiment 1 showed that perception of an unfamiliar phonetic contrast was not less difficult for subjects who had experience with an analogous phonemic distinction in their native language than for subjects without such analogous experience. These results suggest that substantive phonetic experience influences the perception of non-native contrasts, and thus should contribute to a conceptualization of native language-processing skills. In Experiment 2, English listeners' perception of two related nonphonemic place contrasts was not consistently different as had been expected on the basis of phonetic familiarity. A clear order effect in the perceptual data suggests that interactions between different perceptual assimilation patterns or acoustic properties of the two contrasts, or interactions involving both of these factors, underlie the perception of the two contrasts in this experiment. It was concluded that both phonetic familiarity and acoustic factors are potentially important to the explanation of variability in perception of nonphonemic contrasts. The explanation of how linguistic experience shapes speech perception will require characterizing the relative contribution of these factors, as well as other factors, including individual differences and variables that influence a listener's orientation to speech stimuli.