Three-dimensional anorthoscopic perception

When a rotating 3-D wireframe object passes behind a narrow slit, it is often perceived as a 3-D object, even though only a small portion of it is visible at any one instant. This result constitutes a new finding in connection with both anorthoscopic perception and the perception of structure-from-motion.     

Pigeons discriminate continuous versus discontinuous line segments

Three experiments examined various facets of the perception of continuous and discontinuous line segments in pigeons. Pigeons were presented with 2 straight lines that were interrupted by a gap. In some instances, the lines were the same angle and were positioned so that they appeared (to human observers) to form a continuous line. In other instances, the lines were different angles or the same angle but spatially misaligned. The birds were trained to classify each stimulus as continuous or discontinuous using a go/no-go procedure. A series of tests followed in which the birds received novel discontinuous displays made up of familiar line segments, continuous and discontinuous stimuli made up of novel line segments (novel straight lines or curved lines), and familiar displays in which the gap was covered with a gray square. Results from the tests indicated that 2 of the 3 pigeons had learned a continuous-discontinuous categorization and that they appeared to use the relationship between the 2 line segments in discriminating the displays.     

Stimulus frequency in the identification of line segments

Summary In a complete identification experiment line segments with 0, 45, 90, and 135 degrees orientation were exposed tachistoscopically as stimuli. The four stimuli were identified under three successive frequency conditions: In the first condition the stimuli occurred with equal frequency, in the second condition the stimulus probabilities were 0.4, 0.3, 0.2, and 0.1, and in the third condition the stimulus probabilities were 0.2, 0.1, 0.4, and 0.3. A 4×4 stimulus-responses confusion matrix was obtained from each condition and subject. The hit rates obtained for a more frequent stimulus (P=0.4 or 0.3) were higher than the hit rates obtained for a less frequent stimulus, and the same relation held between the proportions of an incorrect response corresponding to a more frequent stimulus and a less frequent stimulus. The confusion matrices were analysed according to the perceptual all-or-none model which allows separation of the effects of stimulus frequency on sensory and on decision processes in identification. Results showed marked effects of stimulus frequency on the decision processes yet no systematic effects on the sensory processes. Attempts to decompose the effects of stimulus frequency on the decision processes failed.Paper presented at the Symposium: Heinrich Düker — Impulse seiner Forschung. 20. Tagung experimentell arbeitender Psychologen, Marburg, 1978     

How the components of speaking rate influence perception of phonetic segments

In two studies we investigated the way in which the components of speaking rate, articulation rate and pause rate, combine to influence processing of the silence-duration cue for the voicing distinction in medial stop consonants. First, we replicated the finding that the articulation rate of a carrier sentence, that is, the rate at which the speech itself is produced, influences how the duration information is used to assign voicing values. Second, and more importantly, the assignment of voicing values was also influenced by the pause rate of the sentence. Thus, the listener adjusts for both articulation rate and pause rate when processing the phonetically relevant information. Finally, the two rate components did not function in an equivalent manner, since changes in articulation rate had considerably more effect on phonetic judgments than did changes in pause rate. Alternative explanations fo the relative weighting of the two variables are discussed.     

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.     

Perception of positional relationships between line segments in eccentric vision

The encoding of positional relationships between pattern elements in eccentric vision was studied with different patterns consisting of the same short line segments in different positions. In each trial two stimulus patterns were flashed one above the other and the subject had to decide whether the patterns were identical or mirror symmetric (experiment 1) or whether the patterns were the same or different (experiments 2 and 3). The ability to discriminate between identical and mirror symmetric patterns was reduced in eccentric vision, even when the patterns were size-scaled according to the cortical magnification factor and thus the patterns were similarly visible at the different eccentricities. The results agree with the notion that eccentric vision is inferior to central vision in tasks which require proper encoding of information about the relative positions of pattern elements.     

Discriminating the integrated orientation of line segments and its statistical efficiencies

Abstract:  We carried out two experiments to investigate both how efficiencies fluctuate due to the experimental conditions and how we determine the representative efficiency among such various efficiencies in the discrimination task of line orientations. In Experiment 1, line segments were displayed simultaneously and dispersed spatially, while in Experiment 2, line segments were displayed sequentially. In both experiments, statistical efficiencies were calculated. In Experiment 1, efficiencies initially increased as stimulus duration increased, and decreased as the number of lines increased to a point where the efficiencies remained almost stable despite additional changes of stimulus duration or number of lines. In contrast, in Experiment 2, efficiencies were stable for almost all numbers of sequentially displayed lines, except for the condition that four lines were displayed in random positions. These stable efficiencies were approximately 50% in Experiment 1 and 30–50% in Experiment 2. We suggest that these stable efficiencies are varied in the context that human and ideal observers would adopt the same strategy regardless of the experimental conditions.     

The misperception of angles: Estimating the vertex of converging line segments

Estimates of the point of intersection of converging line segments depended upon the angle between lines and the orientation of the display. Main conclusion: The tilt of a line is perceptually altered to appear more nearly parallel to the more closely aligned axis, either horizontal or vertical, of an O’s visual field.     

Orientation,length and exposure duration in the identification of line segments

Summary Single line segments titled with 0, 45, 90, and 135 degrees orientation were briefly exposed as stimuli and the subjects had to identify the orientation of a presented line segment. The length of the lines and the exposure duration were varied. The multicomponent theory (Rumelhart, 1970, 1971) was applied to the observed frequencies of a correct response and of some incorrect responses given to a stimulus with a particular orientation, length, and exposure duration. Within the framework of this theory several hypotheses concerning the effects of orientation, length and exposure duration in identification were tested. The main results are: (1) The rate of component detection was higher for the horizontal and vertical orientations than for the two oblique orientations. (2) The number of components in a line segment quite accurately followed a linear function of the line's physical length, and the negatively valued additive constant in this function could not be neglected. (3) The information in the visual information store decayed more rapidly after longer exposure durations and more slowly after shorter exposure durations. These findings are discussed in relation to other research on the subject.     

Attention and perception, memory, and judgment of line length

The literature reports that focused attention alters perceived length of lines. Some tests of this attentional effect require that subjects compare line lengths. This note shows that conceptual confusions inherent in this comparison make the tests invalid.     

Visual detection of line segments: Two exceptions to the object superiority effect

Boundary conditions for the object superiority effect (OSE, target lines embedded in meaningful drawings are more accurately identified than the same targets embedded in nonmeaningful drawings; Weisstein & Harris, 1974) were sought by examining two variables known to affect the word superiority effect. A robust OSE was obtained in both two- and four-alternative tasks with no mask or speed requirement. The OSE was eliminated by either a random masking stimulus composed of dots or lines (Experiment 1) or by requiring speeded identification responses (Experiment 2). An information processing model is proposed to account for the OSE, as well as the exceptions reported herein. It is shown that this model can be modified to deal with the analogous word superiority effect.     

Application of signal detection theory to perception of differences in line length

This paper is an attempt to specify the equinormal model for application to different tasks which are currently used in psychophysics (i.e. phenomenal report, detection, and 2AFC). The same set of stimuli (pairs of horizontal colinear lines) is presented in procedures which differ by the task, the probability of the signal, and the succession of the stimuli of the set. This approach leads to the specification of the sensorial and the decisional aspects of the model.The data indicate that (1) the sensitivity index d' to differences in line length is the same function of the physical stimulus independently of paradigm, as far as the same task is concerned. However, and according to the predictions, its value becomes larger by a factor of 2 in a two alternative forced choice task; (2) d' increases with stimulus exposure time; (3) latency of responses generally decreases with increasing d', and are dissimilar for correct and incorrect responses; (4) when the temporal succession of the stimuli is random the subject's criterion, x_c, is not chosen to optimize the percentage correct, which would require a dependance of criterion upon stimulus amplitude and prior probabilities.     

Line segments are perceived better in a coherent context than alone: An object-line effect in visual perception

In a series of four experiments, observers identified a briefly flashed line segment more accurately when it was part of a drawing that looked unitary and three-dimensional than when the line segment was presented alone. This extends earlier findings of better identification of a line segment when it is part of an apparently unitary, three-dimensional drawing than when it is in a less coherent flat design; and these results demonstrate a visua1 effect analogous to the word-letter effect which uses nonlinguistic materials. Experiment 1 demonstrates the existence of the object-line effect and shows that it does not depend on the presence of a subsequent mask; Experiment 2 shows that the effect holds up with two-altemative forcedchoice presentation; Experiment 3 demonstrates that the effect is not due to bright end points which may occur when the target line appears with a context; and Experiment 4 shows that the effect is as strong when the target line segments occupy widely separated spatial locations as it is when they occupy nearby, potentially confusable locations.     

Lack of degradation in visuospatial perception of line orientation after one night of sleep loss

Sleep deprivation impairs a variety of cognitive abilities including vigilance, attention, and executive function. Although sleep loss has been shown to impair tasks requiring visual attention and spatial perception, it is not clear whether these deficits are exclusively a function of reduced attention and vigilance or if there are also alterations in visuospatial perception. Visuospatial perception and sustained vigilance performance were therefore examined in 54 healthy volunteers at rested baseline and again after one night of sleep deprivation using the Judgment of Line Orientation Test and a computerized test of psychomotor vigilance. Whereas psychomotor vigilance declined significantly from baseline to sleep-deprived testing, scores on the Judgment of Line Orientation did not change significantly. Results suggest that documented performance deficits associated with sleep loss are unlikely to be the result of dysfunction within systems of the brain responsible for simple visuospatial perception and processing of line angles.     

Explanation for neon color effect in achromatic line segments on chromatic inducers based on the multiple interpretation hypothesis

In van Tuijl's neon configurations, an achromatic line segment on a blue inducer produces yellowish illusory color in the illusory area. This illusion has been explained based on the idea of the complementary color induced by the blue inducer. However, it is proposed here that this illusion can be also explained by introducing the assumption that the visual system unconsciously interprets an achromatic color as information that is constituted by transparent and nontransparent colors. If this explanation is correct, not only this illusion, but also the simultaneous color contrast illusion can be explained without using the idea of the complementary color induction.     

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.