Willard L. Brigner

Subjective Contour: Apparent Depth or Simultaneous Brightness Contrast?

The perceptibility of subjective contour in a two-dimensional configuration is shown to vary systematically with the magnitude of simultaneous brightness contrast. Since prior work had suggested depth cues as the basis for subjective contour, depth cues were maintained in all configurations. However, depth cues failed to sustain the perception of subjective contour with a reduction in simultaneous brightness contrast.

Effect of perceived brightness on perceived time

When light intensity demarcating a 1-sec. interval was increased, there was an increase in the perceived duration of the interval. The increase in perceived duration occurred whether the light intensity was physically increased or perceptually increased through brightness enhancement.

Mathematical model for assimilation and contrast in perception of extent.

A mathematical model for assimilation and contrast in the perception of extent is presented, and predictions generated from the model are empirically tested. Implications of the model for the Müller-Lyer illusion are dealt with explicitly, and implications of the model for the Delboeuf, Ebbinghaus, and other illusions of extent are discussed in general terms.

A Correlate to Mach Bands in Perception of Extent

It is demonstrated that contours which vary in extent across space according to the Mach pattern include an increment in apparent extent and a decrement in apparent extent at a position corresponding to the position of Mach bands, i.e., at the inflection points of the pattern. It is also shown that increasing the slope of the gradient of the Mach pattern has an effect upon extent comparable to the effect upon Mach bands. These data are interpreted as supporting the position that lateral inhibitory interaction is involved in the perception of extent. A modification of the Hartline and Ratliff (1956) model for lateral inhibitory interaction is applied, and discrepancies between predictions generated from the model and obtained data provide the basis for recommended changes in the model.

Rotation of Space-Time Plane Predicts a New Illusion of Spatial Displacement

To account for an illusion of succession, it was theorized that the axes of the physical space-time plane were rotated in the process of perceiving. This theoretical rotation of space-time axes led to the prediction and demonstration of an illusion of spatial displacement.

Mathematical model for the filling-in of illusory contour.

It is demonstrated that illusory contour in the shape of a square is perceived lighter when abutted by black horizontal lines and white vertical lines, darker when abutted by white horizontal lines and black vertical lines. These differences in perceived brightness and the spread of brightness, or a filling-in phenomenon, can be modeled by the major product of a column vector and a row unit vector where the order of each vector corresponds to extent and the value of each entry in the column vector corresponds to brightness.

Ebbinghaus Illusion: Effect of Figural Similarity upon Magnitude of Illusion When Context Elements are Equal in Perceived Size

The magnitude of the Ebbinghaus illusion has been reported to be greater when test element and context elements are figurally similar as opposed to figurally dissimilar. In the current investigation with 16 observers, illusion magnitude was greater for a figurally similar configuration even though the context elements of the figurally similar configuration were perceived as smaller than the context elements of a figurally dissimilar configuration. Hence, figural similarity appears to have a prepotent effect in the Ebbinghaus illusion.

EFFECT OF PERCEIVED SIZE UPON PERCEIVED BRIGHTNESS

The increase in perceived size which occurs with an increase in perceived brightness has been known for some time. A reverse effect—an increase in perceived brightness with a decrease in perceived size—is demonstrated.

Visual Image Analysis by Square Wavelets: Empirical Evidence Supporting a Theoretical Agreement between Wavelet Analysis and Receptive Field Organization of Visual Cortical Neurons

It was proposed that the human visual system analyzes images into square wavelets. To test this view, comparisons were made between the perceived similarity-dissimilarity of alphabet letters and the wavelet analyses of those same letters. For the proposal to be considered tenable, the coefficients of the wavelet analysis of similar letters must be similar, and the coefficients of the wavelet analysis of dissimilar letters must be dissimilar. From a selection of 12 letters, four pairs of letters had been reported by Van der Heijden, Malhas, and Van den Roovaart as very similar, and four other pairs of letters dissimilar. Each of the 12 letters was separately depicted in 8×8 matrices, and the signal represented by each of the matrices was analyzed into square wavelets using a new and original procedure which yielded a single set of coefficients for each matrix. Correlations between sets of coefficients were high (r ranged from .88 to 58) for those letter pairs judged high in similarity; correlations were low (r ranged from −02 to .29) for those letter pairs judged low in similarity. When the correlations between the coefficients of wavelets of all eight-letter pairs were compared with the judged similarity-dissimilarity of all eight-letter pairs, the linear agreement was statistically significant. Agreement was found between the neurophysiological mapping of receptive fields of visual cortical neurons and the vectors or the pattern of pluses and minuses which characterized the wavelet analysis. Furthermore, regeneration of the visual image, or the pattern of neural activity representing the image, could be described by a tree-like flow of information among visual cortical neurons which received response data from visual receptive fields, the response data being wavelet coefficients. Results indicate the analysis accurately produces reliable transformations of visual patterns and may be a process used by the visual system.

The problem of the missing wavelet.

A block face was generated by dividing a drawn face into a matrix of rectangular cells and then making the brightness of each cell equal to the average of the brightnesses within the facial area circumscribed by a cell. A wavelet analysis was performed on the numbers representing the brightnesses of the cells in each row of the matrix, and from each row, the wavelet was deleted which corresponded to the fundamental or the lowest frequency sine wave of a complex wave. The appearance of the block face was not substantially altered by the deletion of the wavelet corresponding to the fundamental.