Binocular detection of masked patterns in young and old observers.

A visual pattern embedded in noise is detected appreciably better when the stimulus complex contains interocular cues (dichoptic condition) than when such cues are absent (binoptic condition). In a recent study (F. Speranza, G. Moraglia, & B. A. Schneider, 1995) the authors showed that the relative difference between binoptic and dichoptic thresholds does not change with age. However, older adults showed higher binoptic and dichoptic thresholds, thus suggesting an age-related difficulty with degraded stimulation. In this article the authors first replicated these findings and proceeded next to investigating whether age-related changes in processing efficiency, additive internal noise, and the spatial frequency bandwidth of the detecting filters could account, separately or concurrently, for the elevated thresholds in noise exhibited by the older adults. Results indicate that this increase is not attributable to age-related changes in filter bandwidth or internal noise. Rather, the findings can be explained in terms of a decrease in processing efficiency with age.

Monocular unmasking of noise-embedded patterns.

Binocular disparity cues may help an observer "unmask" a target in a background, thereby enhancing its detectability (e.g., Moraglia & Schneider, 1992). Here, we sought to determine whether similar effects could be produced by monocular displacement cues resulting from a two-frame sequential presentation of a Gabor pattern (a sinusoidal modulation of luminance combined with a Gaussian modulation of local contrast) embedded in an unvarying field of two-dimensional Gaussian noise. The Gabor in the second frame was spatially displaced relative to its location in the first frame; the horizontal displacement corresponded to a phase shift of the peak spatial frequency of the Gabor of 0 degree, 90 degrees, 180 degrees, 360 degrees, or 540 degrees. Monocular detection thresholds for the Gabor were appreciably lower for the 90 degrees, 180 degrees, and 540 degrees shift, than for the 0 degree and 360 degrees values. We explain these findings in terms of a model that constitutes the monocular analog of our summation model of binocular unmasking.

Binocular vision enhances phase discrimination by filtering the background.

Previous studies have shown that the detectability of a noise-masked target can be enhanced under stereoscopic viewing when the target's interocular disparity differs from that of the noise. This enhanced detectability can be accounted for by a model postulating that the binocular system linearly sums the left-eye and right-eye views of a visual scene. This model also predicts enhanced phase discrimination under specifiable interocular disparities of target and noise. Two experiments were conducted in which subjects were asked to discriminate between two luminance patterns (target and foil) that differed only in phase. The target patterns were constructed by summating two vertical sinusoidal gratings in which the phase difference between the higher and the lower spatial frequency gratings was 45 degrees. The foils contained the same two component frequencies, with a phase difference of -45 degrees. Thus, targets and foils were mirror images of one another. The ability of subjects to discriminate between these stereoscopically viewed mirror-image patterns was investigated under two sets of interocular disparities: those that, according to our model, would unmask one or both spatial frequency components, and those that would leave both components masked by the noise. Phase discrimination was enhanced only when both component frequencies of the target and foil were unmasked. The implications of these findings for template-matching and phase-discrimination models of pattern discrimination are considered.

Noise-limited detection in young and old observers.

11 young (M age = 24.3 yr.) and 11 old (M age = 67.4 yr.) observers attempted to detect signals of limited bandwidth in visual noise. The older observers did not perform as well as the young ones. We considered whether, as suggested by a current hypothesis, these differences could be attributed to higher internal additive noise in the elderly observers. The results suggested that internal noise did not differ across the two age groups and that the lower performance of the older observers stemmed instead from reduced processing efficiency.

The effect of stimulus range on perceived contrast: evidence for contrast gain control.

In audition, loudness matches across frequency are affected by the range of stimuli employed at each frequency (e.g., Marks, 1988; Schneider & Parker, 1990). For example, the loudness of a 500-Hz tone that matches the loudness of a 60-dB 2-kHz tone can be changed by as much as 10 to 20 dB by manipulating the range of intensity values to which the listener is exposed. The goal of the present study was to determine whether stimulus range had a similar effect on the perceived contrast of vertical gratings whose spatial frequencies were either 1 or 4 cycles/deg. Viewers judged the perceived contrasts of 1 and 4 cycle/deg gratings intermixed within a session using the method of magnitude estimation. Four different conditions were created by combining either a set of low-contrast or high contrast gratings at one frequency with a broad range of contrasts at the other frequency. When the broad-range set was at 1 cycle/deg, contrast matches across spatial frequencies were unaffected by changing the range of the 4-cycle/deg gratings from low to high. However, when the broad-range set was at 4 cycles/deg, contrast matches were changed by changing the range of the 1 cycle/deg gratings. This asymmetry in the "range effect" was shown to be consistent with the characteristics of the two channels' receptive-field profiles.

Age-related changes in binocular vision: detection of noise-masked targets in young and old observers.

This study investigated the effects of age on binocular unmasking. This term denotes the fact that a visual signal embedded in noise is detected appreciably better when the stimulus complex contains interocular cues (dichoptic condition) than when such cues are absent (binoptic condition). Detection thresholds for two Gabor signals differing in spatial frequency were determined in young and old adults with no identifiable ocular pathologies. The signals were embedded, in both conditions, in two-dimensional Gaussian noise. Binocular Masking Level Differences, defined as the difference between the binoptic thresholds and the dichoptic thresholds, did not change with age; however, the older adults showed higher binoptic thresholds with both signals and higher dichoptic thresholds with only the lower-spatial-frequency signal. For both groups, binoptic and dichoptic thresholds increased with spatial frequency. The implications of these results are discussed.

Binocular vision enhances target detection by filtering the background.

In previous studies the authors have shown that the enhanced detectability exhibited by stereoscopically viewed targets can be accounted for by assuming that the binocular system can linearly summate the left-eye and right-eye views of a visual scene. A model based upon this assumption leads to a variety of predictions concerning the detectability of noise-embedded targets. One such prediction is that the detectability of a target in these conditions is highly orientation specific. A test is reported of such a prediction that can be regarded as counter-intuitive: namely, that the detectability, under stereoscopic viewing conditions, of a patch of sinusoidal grating masked by Gaussian noise should change substantially when the grating, oriented at 45 degrees, is rotated until its orientation becomes -45 degrees. The implications of these results for an understanding of the phenomenon of camouflage breaking are discussed.

C. G. Jung and the psychology of adult development.

Jung can be regarded as a founder of the psychology of adult development and ageing: against the widely held belief that events of decisive import for the formation of an individual's personality occur only within the first two decades of life, he recognized that momentous psychological changes can take place during the second half of life as well. Current appraisals of Jung's contributions in this field tend however to be reductive and simplistic. Accordingly, an attempt is made here to restore some of the complexity of Jung's thought, and to assess its potential towards the attainment of a comprehensive account of the adult condition in contemporary society. This analysis shows that aspects of his views on the developmental course of adulthood enjoy a measure of empirical support. On the other hand, the consideration of some dramatic changes that today's society is increasingly imposing upon the structure of adult life suggests that a revision of some Jungian assumptions about the latter may be in order.

Binocular unmasking with unequal interocular contrast: the case for multiple Cyclopean eyes.

Under certain conditions, the detection threshold for a sinusoidal grating embedded in a noisy background may be an order of magnitude lower when binocular cues are available than when monocular cues only are present. Such binocular unmasking occurs only when the degree of interocular disparity for the target differs from that of the background. Two classes of models have been advanced to account for such unmasking. The first assumes that orientation-specific, spatial frequency channels in each eye encode the amplitude and phase of the spatial frequency component of the pattern the channel is tuned to detect. Thus, a difference in interocular disparity between target and background could result in interocular amplitude and/or phase differences in left- and right-eye spatial frequency channels. When, however, there are no disparity differences between target and background, there will be no interocular differences in amplitude and phase in the left- and right-eye channels. In this model, then, binocular unmasking reflects the binocular system's ability to respond to interocular amplitude and/or phase differences in the patterns presented to the two eyes. In the second class of models, it is assumed that the left- and right-eye patterns are first summed to form a "Cyclopean" eye. In these models, detection depends on the effect this summation process has on the power spectrum of the summated patterns. To decide between these two classes of models, we observed the occurrence of binocular unmasking when (1) the contrast of masker and signal was varied identically in both eyes and (2) the contrast of masker and signal was varied in one eye only. Consistent with our previous research, we found that the results can be accounted for in terms of a linear summation model of binocular unmasking; the alternative interocular phase detection model was disproved. The implications of these findings for binocular contrast summation in the absence of visual noise are discussed.

On binocular unmasking of signals in noise: further tests of the summation hypothesis.

Observers detected the presence of Gabor signals in fields of two-dimensional broadband Gaussian noise encased by a frame of uniform noise. These images, displayed for 1 sec on a t.v. monitor, were seen through a simple-lens stereoscope. While the left and right eye were presented with the same view of the noise frame, the right-eye Gaussian noise field was right-shifted relative to the left-eye's by 20.3 min arc along the horizontal axis. Useful interocular cues concerning signal presence were not available in one set of trials (control condition), the right-eye signal being displaced by the same amount and direction as that of the noise. In another set of trials (experimental condition), such cues were made available by presenting the Gabor signals in exactly corresponding locations in the centres of the two frames. We tested the predictions of a model in terms of which the usefulness of binocular cues for the "unmasking" of the signal rests upon the characteristics of the summed monocular inputs, specifically the signal-to-noise ratio in the summed pattern. The two-dimensional power spectrum for the summed Gaussian noises shows "notches" at specific horizontal- and vertical-frequency intersections where the power density is at or close to zero. If the spectral power in the summed Gabor signal is concentrated at these locations in the experimental condition, the signal should be unmasked. Accordingly, the spatial frequencies and orientation of three Gabor patterns were chosen in such a way that the power density of the summed signals would fit in notches of the power spectrum of the summed noise, while it would overlap with a noise peak for a fourth Gabor signal. The findings were consistent with the summation hypothesis: binocular masking level differences of up to 18 dB were observed, but only for the three signals "falling" in the two-dimensional noise notches.

Binocular unmasking with vertical disparity.

We recently found (Schneider, Moraglia, & Jepson, 1989) that the contrast threshold for the detection of a visual signal in a noisy background can be considerably lower when binocular cues are available then when monocular cues only are present. Here, we investigated the occurrence of binocular unmasking with vertical interocular disparities. Subjects reported about the presence of Gabor signals in fields of two-dimensional broadband Gaussian noise surrounded by a frame of uniform noise. They saw these stimuli through a stereoscope; in all cases, the right-eye noise field was vertically displaced relative to the left one in either an upward or a downward direction, by up to 67.6'. In one condition, the right-eye signal was displaced by an amount equal to that of the noise, so that no opportunities for binocular unmasking existed; in the other, it appeared in exactly corresponding locations in the two fields--here, binocular disparities could be used to unmask the signal. Enhanced signal detectability, by up to 12.7 dB, was observed in the latter case for both directions of displacement, but only for displacements of 13.52' and only when the signal's orientation was horizontal. We argue that these effects result from the summation of monocular inputs carried out by linear binocular mechanisms.

Effects of direction and magnitude of horizontal disparities on binocular unmasking.

Conditions under which binocular unmasking (BU), as an analogue of binaural unmasking, occurs have been explored. Observers were to detect through a stereoscope a Gabor signal in patches of two-dimensional broadband gaussian noise surrounded by a frame of uniform noise. The right-eye gaussian field was displaced relative to the left eye so that it appeared either in front of or behind the frame. Performance when signal disparity was equal to that of the noise--a condition functionally equivalent to monocular processing--was compared to that obtained when signal disparity was zero--a case in which BU should occur. Enhanced signal detectability of up to 12 dB and of nearly constant magnitude was observed in the latter condition when uncrossed disparities of up to 67.60 min visual angle and display durations of 1 s were employed. Signal detectability declined appreciably with increasing disparity (both crossed and uncrossed) when display duration was reduced to 90 ms, thus preventing the occurrence of compensatory vergence eye movements. It is suggested that BU effects may result from a process of linear summation of monocular inputs.

Visual search: spatial frequency and orientation.

Observers searched for a Gaussian-windowed patch of sinewave grating (Gabor pattern) through displays containing varying numbers of other such patterns (distractors). When the spatial frequencies of target and distractors differed by +/- 2 octaves and their orientations by +/- 60 degrees, the search proceeded spatially in parallel irrespective of whether the target could be discriminated in terms of spatial frequency differences alone, orientation differences alone, or their combination. However, when target and distractors differed by only +/- .5 octave in spatial frequency and by +/- 15 degrees in orientation, the search was serial and self-terminating, again irrespective of the nature of the target-distractor differences. These findings show that, contrary to some suggestions, the preattentive detection of targets defined by conjunctions of spatial frequency and orientation may occur, but only when the spectral distance between target and distractors allows their encoding by independent mechanisms.

Display organization and the detection of horizontal line segments.

Observers searched for a horizontal line segment through displays containing varying numbers of elements differing from the target and from each other in terms of orientation. These elements were always positioned on imaginary concentric circles centered in the middle of the display. They were allocated to these positions either randomly or in such a way that their orientation was equal to that of the tangent to the circle at that position. The search for the target line appeared to proceed spatially in parallel with the latter class of displays, and serially with the former. These findings are explained and discussed within the context of the attentive-preattentive dichotomy that characterizes spatial vision.

Visual search along the colour dimension.

Subjects searched for a chromatic target among coloured background items. With low target-background chromatic similarity, response latencies remained uniformly short whether the target was present or not and whether the items were chromatically homogeneous or not. Latencies increased with increases in target-background similarity and were longest with heterogeneous backgrounds, with which the effects of trial also became manifest. We employed Treisman's model of visual search to account for these findings. In particular, we suggest that similarity increases forced a shift from a preattentive to an attentive search, the latter being importantly shaped by the background's level of chromatic variance.

Binocular unmasking: an analog to binaural unmasking?

A visual analog to binaural unmasking was explored. The observer's task was to detect, under stereoscopic viewing conditions, an apertured sinusoidal grating added to a square patch of visual noise. In the experimental condition, the square patch of noise was presented within a frame such that the right-eye noise was a shifted version of the left-eye noise. Because of the disparity in the noise images, subjects perceived, under stereoscopic viewing conditions, that the noise patch was located behind the frame. When sinusoidal signals were added to this noise patch, the signals were clearly more detectable when the signal disparity was zero than when the signal disparity equaled that of the noise patch, demonstrating the existence of visual unmasking. Hence, under appropriate circumstances, binocular processing, in addition to providing information about depth, can also enhance the detectability of visual patterns.

The concept of spatial frequency channels cannot explain some visual masking effects.

Visual masking is assumed to be predictable by the degree to which mask and signal spatial frequency amplitudes are similar. In this masking experiment we have clearly shown this not to be the case by studying the effects of factorial combinations of signal-mask amplitude and phase spectra. Results show that the amplitude spectra characteristics do not predict masking, and a better predictor of these results appears to be the correlations between the mask and signal's luminance profiles. These results, therefore, show that the spatial similarity between two images, as may be processed by "spatial frequency channels" cannot be determined by the similarities between these channel outputs as defined by the (output) modulated amplitudes.

Is pattern masking predicted by the cross-correlation between signal and mask?

We sought to determine whether the cross-correlation between signals and masks consisting of Gaussian modulated grating patterns is consistent with observed psychophysical masking effects. Our experimental results support this relationship, and suggest further specifications for the determinants of pattern masking effects.

On the detection of signals in non-white noise.

We have studied the detection, by human observers, of suprathreshold bandlimited signals embedded at various locations in non-white, Gaussian filtered noise. Detection models based upon the direct cross-correlation between the signal and the noise image (matched filtering) cannot account for the results of our experiments. Our findings point instead at a detection process occurring at the level of signal decomposition, and jointly determined by: (a) the differential outputs of discrete, bandlimited spatial analyzers selectively responsive to different components of the signal; and (b) variable detection rules adaptively related to such outputs and to the type of signal information available to the observer.