Size and distance judgments under reduced conditions of viewing

Magnitude estimations of the size and distance of a variable relative to a standard were obtained in the absence of distance cues. Estimates were provided by different groups under three conditions: (a) physical size and distance variant, visual angle of the variable constant and equal to the standard, (b) physical size constant, physical distance and visual angle of variable changing, and (c) physical distance constant, physical size and visual angle of the variable changing. The results in both experiments were very similar. In each case both size and distance estimates conformed to relative visual angle. The results are applied to an analysis of size-matches that are obtained when distance cues are eliminated.     

Auditory saltation in the vertical midsagittal plane

Auditory saltation is an illusion in which a train of clicks, the first half of which is presented at one location and the other half of which is presented from a second location, is perceived as originating not only from the anchor points, but also from locations between them. That is, intermediate members of the series of clicks have their spatial locations systematically misperceived. In the present study, auditory saltation was examined for the first time in the vertical midsagittal plane. Subjects rated the perceived continuity of motion for 8-click trains systematically varied in inter-click interval (ICI), direction of motion (up, down), and trial type ('saltation' versus 'real' motion). In all listeners, saltation stimuli supported robust saltation, but only for trials with ICIs less than about 120 ms. Real motion was rated as continuous for all ICIs. These data indicate that the auditory-saltation illusion can exploit monaural stimulus cues for source location in the generation of the illusory motion percept.     

Colour constancy with change of viewing distance under water

Colour constancy is commonly considered to be the product both of high-order (cognitive) and of lower-order (retinal) mechanisms. A study is reported of colour appearance in situations where the spectral radiance of an object changes significantly with viewing distance. Subjects were instructed to match the colour appearance of a number of coloured tiles in air and at various viewing distances in different types of water. Colour-constancy ratios were calculated by comparing the visual data with simultaneously obtained spectroradiometric and photometric data. The obtained constancy ratios were attributed to the role of distance estimation in the determination of colour appearance, an effect that is presumably masked under normal viewing conditions, where long viewpaths are necessary to produce significant radiance changes. A similarity to the size-distance invariance hypothesis is noted.     

Effects of distance between objects and distance from the vertical axis on shape identity judgments

In three experiments, we independently manipulated the angular disparity between objects to be compared and the angular distance between the central axis of the objects and the vertical axis in a mental rotation paradigm. There was a linear increase in reaction times that was attributable to both factors. This result held whether the objects were rotated (with respect to each other and to the upright) within the frontal-parallel plane (Experiment 1) or in depth (Experiment 2), although the effects of both factors were greater for objects rotated in depth than for objects rotated within the frontal-parallel plane (Experiment 3). In addition, the factors interacted when the subjects had to search for matching ends of the figures (Experiments 1 and 2), but they were additive when the ends that matched were evident (Experiment 3). These data may be interpreted to mean that subjects normalize or reference an object with respect to the vertical upright as well as compute the rotational transformations used to determine shape identity.     

Absolute distance perception to locations off the ground plane

Using vision, humans can accurately judge distances to locations on the ground surface up to distances of at least 20 m. Most theories of depth perception assume that this ability is associated with the fact that we live in a terrestrial world in which locations of interest often appear on the ground and for which feedback about distance is often available from nonvisual sources such as walking. Much less is known about the ability of humans to judge absolute distances to locations other than on or supported by the ground plane beyond a few meters, at which point binocular stereo provides at best limited information about distance scaling. We show that one commonly used action measure for probing absolute distance perception exhibits accurate performance, even for targets located on the ceiling of a large room. We follow this with evidence that distance to ceiling locations is recovered with a mechanism that depends, at least in part, on the angle from the line of sight to the target location and a gravity-based frame of reference.     

Perception of self-tilt in a true and illusory vertical plane

A tilted furnished room can induce strong visual reorientation illusions in stationary subjects. Supine subjects may perceive themselves upright when the room is tilted 90 degrees so that the visual polarity axis is kept aligned with the subject. This 'upright illusion' was used to induce roll tilt in a truly horizontal, but perceptually vertical, plane. A semistatic tilt profile was applied, in which the tilt angle gradually changed from 0 degrees to 90 degrees, and vice versa. This method produced larger illusory self-tilt than usually found with static tilt of a visual scene. Ten subjects indicated self-tilt by setting a tactile rod to perceived vertical. Six of them experienced the upright illusion and indicated illusory self-tilt with an average gain of about 0.5. This value is smaller than with true self-tilt (0.8), but comparable to the gain of visually induced self-tilt in erect subjects. Apparently, the contribution of nonvisual cues to gravity was independent of the subject's orientation to gravity itself. It therefore seems that the gain of visually induced self-tilt is smaller because of lacking, rather than conflicting, nonvisual cues. A vector analysis is used to discuss the results in terms of relative sensory weightings.     

Apparent distance in a horizontal plane with tactile-kinesthetic stimuli

In the study of active tactile-kinesthetic space perception apparent distance has been found to vary as a function of the direction of the line segment in a horizontal plane. The present data indicate that the error is not consistently related to the same frame of reference as the visual illusion. Rather, with movement of the extended arm to determine the relative distances between pairs of points, radial distances are overestimated in relation to tangential ones, whether parallel or perpendicular to the medial plane. Interpretations are in terms of kinesthetic stimulus patterns and the structure of perceptual representation.     

Change of preferences under time pressure: choices and judgements

Students made choices between student apartments judged to be equally attractive. When asked to choose the best apartment in each pair of alternatives, choices made by a group under time pressure were significantly different from those made by another group under no time pressure. The effect was so strong that preference reversals were obtained which could be explained by subjects over-evaluating negative aspects on the most important attribute under time pressure.     

Localization of sound in the vertical plane with and without high-frequency spectral cues

Binaural localization of 3.0-kHz high- and lowpass noise presented in the median vertical plane (MVP) and lateral vertical plane (LVP) was investigated. We anticipated superior performance when localizing the highpass noise hy virtue of the availability of pinna cues. The viability of this supposition was strengthened by monaural localization tests in which performance proficiency for the highpass noise exceeded that for the lowpass noise (p < .01). The main result showed that binaural localization of proficiency for highpass noise surpassed that for lowpass noise for all listening conditions (p < .01). However, the importance of binaural temporal and level differences in vertical-plane localization was demonstrated by the highly respectable performances when the lowpass noise was presented in the LVP. Data from binaural localization in the MVP and monaural localization in the LVP suggested that the influence of pinna cues diminishes for source elevations above 45°.     

Horizontal and vertical distance perception: The discorded-orientation theory

We sought the conditions where the horizontal—vertical illusion (HVI) takes place outdoors in an open field. Longitudinal distance from a subject to a building wall was adjusted to appear equal to the vertical or horizontal distance on the wall. To examine validity of previous theories (physiology, frame, depth, and gravity theories), boundary of visual field (ellipse and circle), bodily orientation (upright and lying), and orientation of visual objects (normal, 90°-tilted, and inverse) were manipulated in eight experiments. These three independent variables affected the HVI effects, but their effects were not explained by the previous theories. We therefore proposed a model on the basis of discord among the retinal, visual, and gravitational orientations. We also found that longitudinal distance was adjusted as being consistently larger than the standard distance. This result was explained by the reduction of cues to distance and the HVI effect.     

The overestimation of vertical distance and slope and its role in the moon illusion

Six experiments were conducted to test the hypothesis that overestimation of vertical distance is a pervasive phenomenon. The experiments involved judgments of: (a) vertical distance looking upward; (b) vertical distance looking downward; (c) the slope of a real hill; (d) the recalled slopes of streets; (e) the magnitudes of angles drawn on paper; (f) the distances to afterimages projected into the sky. The results showed that a very strong illusion of overestimation of both vertical distance and slope occurred in all situations except for the judgments of drawn angles by males. Furthermore, in five of the six experiments females showed a greater amount of the illusion than males. The discussion pointed out the difficulty of explaining the moon illusion by the assumptions of a flattened sky surface and Emmert’s law in light of the data.     

The symbolic distance effect for alphabetic order judgements: A subjective report and reaction time analysis

The time needed to decide whether a pair of letters is in the correct alphabetic order varies inversely with alphabetic separation. This is an example of a phenomenon generally found with the comparison of ordered symbols or concepts, called the symbolic distance effect (Moyer and Bayer, 1976). It is argued that when letters are compared, an important determinant of this effect is the degree to which subjects subvocally run-through parts of the alphabet to determine the correctness of the order of a stimulus pair. A trial-by-trial introspection procedure coupled with reaction time measurements is used in the present experiment, in which letter order judgements were made over a range of separations. RTs increased with increasing number of letters in the reported run-through. At small letter separations, run-through occurred more frequently, and this was found to be the basis of the symbolic distance effect. For trials on which no run-through was reported the symbolic distance effect was absent. The data are summarized as a model in which comparisons are made from directly available order information from memory, or with an additional run-through process. The details of the run-through process suggest that groupings learned in childhood are probably involved in the selection of the starting letter for run-through.     

Localization of sound in the vertical plane with and without high-frequency spectral cues.

Binaural localization of 3.0-kHz high- and lowpass noise presented in the median vertical plane (MVP) and lateral vertical plane (LVP) was investigated. We anticipated superior performance when localizing the highpass noise by virtue of the availability of pinna cues. The viability of this supposition was strengthened by monaural localization tests in which performance proficiency for the highpass noise exceeded that for the lowpass noise (p less than .01). The main result showed that binaural localization of proficiency for highpass noise surpassed that for lowpass noise for all listening conditions (p less than .01). However, the importance of binaural temporal and level differences in vertical-plane localization was demonstrated by the highly respectable performances when the lowpass noise was presented in the LVP. Data from binaural localization in the MVP and monaural localization in the LVP suggested that the influence of pinna cues diminishes for source elevations above 45 degrees.     

Mechanisms controlling head stabilization in the elderly during random rotations in the vertical plane

Frequency-related response characteristics of the mechanisms controlling stabilization of the head in 10 elderly subjects were compared with response characteristics in 8 young adults. Angular velocity of the head with respect to the trunk and EMG responses of 2 neck muscles were recorded in 10 seated subjects during pseudorandom rotations of the trunk in the sagittal plane at frequencies of 0.35 to 3.05 Hz. Subjects were required to actively stabilize their heads with (VS) and without (NY) visual feedback so that voluntary mechanisms and the influence of vision could be tested. Reflex mechanisms were examined when subjects were distracted by a mental calculation task during rotations in the dark (MA). Age emerged as an influential factor in the performance of head stabilization mechanisms, and decrements in performance were even more pronounced in the older as compared with younger elderly subjects. Age effects could be seen in the (a) diminished ability to voluntarily stabilize the head, particularly with the absence of vision, (b) impaired ability to stabilize the head when cognitively distracted, and (c) appearance of a resonant response of the head. Control of head stabilization shifted from reflex mechanisms to system mechanics, probably as a result of age-related changes in the integrity of the sensory systems. The elderly's system mechanics could not effectively compensate for the disturbances, however, and instability was the result.     

The influence of the acoustic context on vertical sound localization in the median plane

The influence of background sounds (frames) on vertical localization of single sound sources (targets) was examined in four experiments. Loudspeakers (five targets and four frames) were positioned in the median plane, ranging from +30 degrees to -30 degrees above and below the subject's ear level. The subjects determined the vertical position of the targets by either verbal judgments or manual pointing. Frame and target sounds were presented concurrently or successively with a 1-sec interval; both consisted of (1) 300-Hz square waves, (2) noise, or (3) targets of noise and frames of 300-Hz square waves. Particularly in the second condition, the subjects consistently shifted the apparent target positions away from the frame locations. This contrast effect persisted even 1 sec after the offset of the frames. No effect was found with different waveforms for the frame and the target. Results are related to recent findings indicating a similar effect in the azimuthal dimension. Possibly the effect is based on a mechanism in which the auditory system adapts to recently heard sound source positions.     

Discounting in causality and covariation judgements

In two experiments, humans were asked to judge the strength of a moderate contingency between a cue and an outcome in the presence of a second strong contingency between another cue and the outcome. The first experiment replicated the discounting effect whereby a strong contingency causes subjects to reduce or discount judgements of a moderate contingency. This experiment used a video-game procedure in which subjects camouflaged a tank to make it safe from mines. The second causal cue was the presence or absence of a spotter plane. Experiment 1 also ruled out the possibility that judgements might be determined by the number of co-occurrences of the cue and outcome as opposed to the level of contingency. The second experiment used an abstract scenario in which discounting was demonstrated when subjects were asked to judge the relationship between the occurrence of geometric objects. The instructions were neutral to discourage causal hypotheses. These results support the notion that judgements result from associative or connectionist processes and not from a two-step cognitive retrospective process in which an estimate of covariation is calculated between cue and outcome and then in a second step this information is used in a normative manner when a decision is made.