The categorical representation of visual pattern information by young infants

The present research studied 3- and 4-month-old infants' ability to acquire two categories simultaneously. A familiarization-novelty preference procedure and geometrical form categories were used in all experiments. In Experiments I and 3, infants were familiarized with either a single form category, two form categories, or a single form category plus a set of forms that did not define a category. The results showed that, despite increased attentional and memorial demands, presentation of an additional form category did not harm the efficiency of categorization (Experiment 1) and changed the representation of the form category information from exemplars to a prototype (Experiment 3). Contrasting form information that was not categorical in structure decreased the infant's ability to recognize new members of the single familiar category (Experiment 1) and hindered the infant's ability to form a categorical representation (Experiment 3). The categorization behavior observed in Experiment 1, as indexed by the generalization of habituation to novel forms from a familiar category, was shown not to be a consequence of the inability to discriminate between individual members from the familiar form category (Experiment 2). The implications of these results for cognitive development are discussed.     

Internal representation of visual texture as the basis for the judgment of similarity

The relationship between Fourier spectra of visual textures (represented both by the actual frequency components and by the response of four hypothetical channels selectively sensitive to spatial frequency) and the perceptual appearance of the textures was investigated. Thirty textures were synthesized by combining seven spatial frequencies whose amplitudes were randomly chosen and then scaled to give an overall contrast of .9. Similarity judgments were collected using both the method of triadic comparison (two subjects, 4,060 trials each) and the method of paired comparison (six subjects, 435 trials each). The similarity judgments were subjected to MDSCAL and INDSCAL dimensions were found to be optimally oriented in terms of spatial frequency information without rotation. The seven spatial frequency components accounted for 90.6% of the variance in the 3-D INDSCAL space, while the four channels accounted for 91.8% of the variance in the first two dimensions. The data further suggest that the four channels may interact in an opponent process manner. The results support the idea that the visual internal representation of stimuli is based on spatial frequency analysis rather than feature extraction.     

The representation of visual scenes

The visual world exists all around us, yet this information must be gleaned through a succession of eye fixations in which high visual acuity is limited to the small foveal region of each retina. In spite of these physiological constraints, we experience a richly detailed and continuous visual world. Research on transsaccadic memory, perception, picture memory and imagination of scenes will be reviewed. Converging evidence suggests that the representation of visual scenes is much more schematic and abstract than our immediate experience would indicate. The visual system may have evolved to maximize comprehension of discrete views at the expense of representing unnecessary detail, but through the action of attention it allows the viewer to access detail when the need arises. This capability helps to maintain the 'illusion' of seeing a rich and detailed visual world at every glance.     

Information representation in visual images

How information is represented in visual images was explored in five experiments where subjects judged whether or not various properties were appropriate for given animals. It took more time to evaluate an animal when the subjective image of it was small, whether size was manipulated directly or indirectly (e.g., by having a target animal imaged at the correct relative size next to an elephant or a fly). More time also was required if the animal was imaged in a relatively “complex” environment (next to 4 vs. 2 digits painted on an imaginary wall, or next to a 16 cell vs. 4 cell matrix). Finally, subjectively larger images required more time to evoke than smaller images. These results support a constructivist notion of imagery, and the idea that images may act as ‘analogues’ to percepts.     

Internal representation of simple temporal patterns

In this study the imitation of several periodically repeating simple temporal patterns consisting of two or more intervals varying in their duration ratios has been investigated. The errors that subjects typically made in their imitations and the systematic changes that occurred during repeated imitations indicate that both musically trained and untrained subjects map temporal sequences onto an interval structure the nature of which is revealed by studying which patterns are correctly and which incorrectly reproduced. A "beat-based" model for the perception of temporal sequences is proposed. This model states that the first step in the processing of a temporal sequence consists of a segmentation of the sequence into equal intervals bordered by events. This interval is called the beat interval. How listeners select this beat interval is only partly understood. In a second step, intervals smaller than the beat interval are expressed as a subdivision of the beat interval in which they occur. The number of within-beat structures that can be represented in the model is, however, limited. Specifically, only beat intervals that are subdivided into either equal intervals or intervals in a 1:2 ratio fit within the model. The partially hierarchical model proposed, though in need of further elaborations, shows why the number of temporal patterns that can be correctly conceptualized is limited. The relation of the model to other models is discussed.     

Cooperative representation of visual borders.

Recently it has been reported that the visual cortical cells which are engaged in cooperative coding of global stimulus features, display synchrony in their firing rates when both are stimulated. Alternative models identify global stimulus features with the course spatial scales of the image. Versions of the Munsterberg or Café Wall illusions which differ in their low spatial frequency content were used to show that in all cases it was the high spatial frequencies in the image which determined the strength and direction of these illusions. Since cells responsive to high spatial frequencies have small receptive fields, cooperative coding must be involved in the representation of long borders in the image.     

Spatial representation of a two-dimensional pattern

The purpose of this study was (a) to determine if vision and kinesthesis contribute differentially to the coding of a specific two-dimensional pattern and (b) to identify the effect of repetition on the spatial representation of this pattern. The reproductions of a specific pattern presented visually were compared with those of a pattern presented kinesthetically. The results showed that vision and kinesthesis had contributed equally to the coding of the directional components of the pattern. However, there was dominance of visual information over kinesthetic information when coding the distance between the intersecting points of the pattern, especially at the beginning of the process. Generally speaking, the visual or kinesthetic repetition, or both, have increased favourably the precision with which a specific pattern was reproduced in distance and direction.     

The time course of abstract visual representation

Studies in change blindness re-enforce the suggestion that veridical, pictorial representations that survive multiple relocations of gaze are unlikely to be generated in the visual system. However, more abstract information may well be extracted and represented by the visual system. In this paper we study the types of information that are retained and the time courses over which these representations are constructed when participants view complex natural scenes. We find that such information is retained and that the resultant abstract representations encode a range of information. Different types of information are extracted and represented over different time courses. After several seconds of viewing natural scenes, our visual system is able to construct a complex information-rich representation.     

The structure of visual pattern associates and pattern goodness

Two tasks were used with a total set of 126 dot patterns. In one task Ss rated the goodness of each pattern. In another task they produced a dot pattern as an associate to each of the patterns used as a stimulus. The distributions of the associates suggest that the total set of patterns is both partitioned and nested. Groups defined by rotation and reflection are partitioned, thus kept intact. These groups in turn form a series of nested subsets., Both partitioning and nesting produce subsets of different size. The size of these subsets is related to pattern goodness, with good patterns coming from small subsets.     

The spatiotopic representation of visual objects across time

Each eye movement introduces changes in the retinal location of objects. How a stable spatiotopic representation emerges from such variable input is an important question for the study of vision. Researchers have classically probed human observers' performance in a task requiring a location judgment about an object presented at different locations across a saccade. Correct performance on this task requires realigning or remapping retinal locations to compensate for the saccade. A recent study showed that performance improved with longer presaccadic viewing time, suggesting that accurate spatiotopic representations take time to build up. The first goal of the study was to replicate that finding. Two experiments, one an exact replication and the second a modified version, failed to replicate improved performance with longer presaccadic viewing time. The second goal of this study was to examine the role of attention in constructing spatiotopic representations, as theoretical and neurophysiological accounts of remapping have proposed that only attended targets are remapped. A third experiment thus manipulated attention with a spatial cueing paradigm and compared transsaccadic location performance of attended versus unattended targets. No difference in spatiotopic performance was found between attended and unattended targets. Although only negative results are reported, they might nevertheless suggest that spatiotopic representations are relatively stable over time.     

Constraining the neural representation of the visual world

Understanding the perception of all but the most impoverished and artificial scenes presents a different and probably far greater challenge from understanding face recognition, reading, or identification (or even categorization) of single objects. Central issues in the interpretation of structured objects and scenes are reviewed, starting with fundamentals such as the meaning of seeing. A theoretical approach to this formidable task is outlined, motivated by some recent developments in neuroscience and neurophilosophy.     

Ensemble representation and the contents of visual experience

Philosophical Studies - The on-going debate over the ‘admissible contents of perceptual experience’ concerns the range of properties that human beings are directly acquainted with in...     

Coding theory of visual pattern completion

It is possible to construct a line drawing that represents one object partly hidden behind another, and most subjects complete the interrupted figure and see the hidden object as whole. This article is addressed to two problems: (a) What are the necessary and sufficient conditions for such figural completion to occur, and (b) exactly what will be seen behind the occluding figure---that is, what completion will be made? Leeuwenberg's coding model for line drawings was used to analyze a number of such figures, along with the hypothesis that figural completion occurs whenever it results in a simplification of final code of the whole figure. Data from previous experiments along with results from two new experimental studies were collected and shown to agree with this hypothesis. Of various possible figural completions or "mosaic" interpretations, subjects chose the ones resulting in the simplest overall code. However, the above conclusions are correct only if "simple" is precisely defined as the smallest information load in a completely reduced code. Other possible theories of figural completion, both structuralist and Gestalt, may invoke familiarity, particular "cues," like T-shaped intersections, simplicity of the hidden figure, symmetry, and good continuation. All such possibilities were considered in the experiments and shown to fail, wrongly predicting at least one figure. The coding-theory analysis, on the other hand, made correct predictions for all of the 25 figures used.     

Systematic angular biases in the representation of visual space

Representing spatial information is one of our most foundational abilities. Yet in the present work we find that even the simplest possible spatial tasks reveal surprising, systematic misrepresentations of space—such as biases wherein objects are perceived and remembered as being nearer to the centers of their surrounding quadrants. We employed both a placement task (in which observers see two differently sized shapes, one of which has a dot in it, and then must place a second dot in the other shape so that their relative locations are equated) and a matching task (in which observers see two dots, each inside a separate shape, and must simply report whether their relative locations are matched). Some of the resulting biases were shape specific. For example, when dots appeared in a triangle during the placement task, the dots placed by observers were biased away from certain parts of the symmetry axes. But other systematic biases were not shape specific, and seemed instead to reflect differences in the grain of resolution for different regions of space. For example, with both a circle and even a shapeless configuration (with only a central landmark) in the matching task, observers were better at discriminating angular differences (when a dot changed positions around the circle, as opposed to inward/outward changes) in cardinal versus oblique sectors. These data reveal a powerful angular spatial bias, and highlight how the resolution of spatial representation differs for different regions and dimensions of space itself.

     

The visual representation of three-dimensional, rotating objects.

Depth rotations can reveal new object parts and result in poor recognition of "static" objects (Biederman & Gerhardstein, 1993). Recent studies have suggested that multiple object views can be associated through temporal contiguity and similarity (Edelman & Weinshall, 1991; Lawson, Humphreys & Watson, 1994; Wallis, 1996). Motion may also play an important role in object recognition since observers recognize novel views of objects rotating in the picture plane more readily than novel views of statically re-oriented objects (Kourtzi & Shiffrar, 1997). The series of experiments presented here investigated how different views of a depth-rotated object might be linked together even when these views do not share the same parts. The results suggest that depth rotated object views can be linked more readily with motion than with temporal sequence alone to yield priming of novel views of 3D objects that fall in between "known" views. Motion can also enhance path specific view linkage when visible object parts differ across views. Such results suggest that object representations depend on motion processes.     

Size scaling in visual pattern recognition

Human visual recognition on the basis of shape but regardless of size was investigated by reaction time methods. For successive matching of random figures, reaction time increased linearly with the linear size ratio of stimulus pairs. For single-character classification, reaction time increased with divergence between cued size format and stimulus format such that for character nonrepetitions, the increment in latency was approximately proportional to the logarithm of the linear size ratio of the two formats. However, when reactions to character repetitions were faster than those to nonrepetitions, the repetition reaction time function was similar to that for successive matching of random figures. The results suggested two processes of size scaling: mental-image transformation and perceptual-scale transformation. Image transformation accounted for matching performance based on visual short-term memory, whereas scale transformation accounted for size invariance in recognition based on comparison against visual representations in long-term memory.