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PubMed2004

The opioid receptor like-1 receptor agonist Ro 64-6198 (1S,3aS-8-2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one) produces a discriminative stimulus in rats distinct from that of a mu, kappa, and delta opioid receptor agonist cue.

Male Wistar rats were trained to discriminate either the opioid receptor like (ORL)-1 receptor agonist Ro 64-6198 (1S,3aS-8-2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one) or morphine from saline using a two-choice, food reinforced, operant procedure. Acquisition of Ro 64-6198 discrimination was relatively slow (mean trials to criterion 113 +/- 6), and a final 4 mg/kg dose (initial training dose 2 mg/kg) was required to establish appropriate stimulus control. In comparison, a separate group of rats attained a morphine (2 mg/kg) discrimination in 44 +/- 4 trials. In tests of substitution, Ro 64-6198 produced a dose-related generalization to its own cue (ED(50) of 1.1 mg/kg i.p.), yet only weakly generalized to the morphine cue (19% at 10 mg/kg i.p.). In contrast, morphine generalized completely to the morphine cue (ED(50) of 0.7 mg/kg s.c.), yet only partially generalized to the Ro 64-6198 cue (40% at 6 mg/kg s.c.). The kappa opioid receptor agonist U50,488 [trans-3,4-dichloro-N-methyl-N(2-[1-pyrrolidinyl]cyclohexyl) benzeneacetamide methanesulfonate] (0.3-6 mg/kg s.c.) and the delta opioid receptor agonist SNC-80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide] (0.3-6 mg/kg i.p.) failed to evoke significant generalization to either cue. The mu opioid receptor agonists codeine (0.3-20 mg/kg) and buprenorphine (0.01-1 mg/kg) completely generalized to the morphine cue, but only buprenorphine partially generalized to the Ro 64-6198 cue. Naloxone pretreatment completely blocked the morphine cue (ED(50) of 0.005 mg/kg s.c.), yet only weakly attenuated the Ro 64-6198 cue at 0.3 mg/kg. Finally, the selective ORL-1 antagonist J-113397 [1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1, 3-dihydro-2H-benzimidazol-2-one] completely blocked the Ro 64-6198 cue at a dose (30 mg/kg i.p.) that had no effect against the morphine cue. The present studies demonstrate that rats may be trained to discriminate Ro 64-6198 from saline, and the pharmacological characteristics of this cue are most consistent with ORL-1 receptor activation.

Animals↗
PubMed1997

Cues that hippocampal place cells encode: dynamic and hierarchical representation of local and distal stimuli.

Hippocampal place fields were recorded as rats explored a four-arm radial maze surrounded by curtains holding distal stimuli and with distinct local tactile, olfactory, and visual cues covering each arm. Systematic manipulations of the individual cues and their interrelationships showed that different hippocampal neurons encoded individual local and distal cues, relationships among cues within a stimulus set, and the relationship between the local and distal cues. Double rotation trials, which maintained stimulus relationships within distal and local cue sets, but altered the relationship between them, often changed the responses of the sampled neural population and produced new representations. After repeated double rotation trials, the incidence of new representations increased, and the likelihood of a simple rotation with one of the cue sets diminished. Cue scrambling trials, which altered the topological relationship within the local or distal stimulus set, showed that the cells that followed one set of controlled stimuli responded as often to a single cue as to the constellation. These cells followed the single cue when the stimulus constellation was scrambled, but often continued firing in the same place when the stimulus was removed or switched to respond to other cues. When the maze was surrounded by a new stimulus configuration, all of the cells either developed new place fields or stopped firing, showing that the controlled stimuli had persistent and profound influence over hippocampal neurons. Together, the results show that hippocampal neurons encode a hierarchical representation of environmental information.

Animals↗
PubMed2001

Long-lasting rebound cue effects following single doses of nicotine and amphetamine: implications for understanding tolerance.

RATIONALE: Previous drug-discrimination studies have, with the exception of nicotine (NIC), demonstrated tolerance to the cue effects of a broad range of drugs of abuse. Barrett et al. have shown that tolerance to a drug's cue properties reflects drug-induced rebound shifts in the discrimination baseline and not a weakened or less salient cue. OBJECTIVES: The objective of the present study was to use a discrimination task sensitive to bidirectional cue changes to characterize the interoceptive cues associated with both the primary and rebound cues produced by nicotine in an attempt to understand why a recent study by Shoaib et al. failed to observe tolerance to the nicotine cue. METHODS: Since dopamine (DA) has been implicated in mediating the NIC cue, rats were trained to discriminate between 0.25 mg/kg amphetamine (AMPH), an indirect DA agonist, and 0.033 mg/kg haloperidol (HAL), a DA antagonist at the D2 receptor site. Training doses were chosen so that rats responded about equally on both levers when tested on saline (SAL) following acquisition. This procedure provided a behavioral baseline to assess NIC-related changes along a presumed continuum of DA-mediated cues. Following acquisition of the discrimination: (i) NIC substitution tests were conducted, (ii) rats were tested for lever choice at intervals from 2 h to 48 h following treatment with single doses of 0.25 mg/kg and 0.50 mg/kg NIC, and (iii) rats were challenged with test doses of NIC during a period of NIC rebound. RESULTS: (i) NIC substituted for AMPH in a dose- dependent manner. (ii) At short intervals after treatment with 0.25 mg/kg and 0.50 mg/kg NIC, rats responded primarily on the AMPH lever followed by a shift to predominant responding on the HAL lever 16-24 h post-treatment, before returning to predrug levels. (iii) No evidence was observed for acute tolerance to NIC. CONCLUSIONS: The robust and long-lasting rebound cues associated with training level doses of NIC suggest that maximal tolerance would likely develop to the NIC cue during the acquisition phase of the conventional NIC-saline discrimination study.

Amphetamine↗
PubMed2004

Interaction of color and geometric cues in depth perception: when does "red" mean "near"?

Luminance and color are strong and self-sufficient cues to pictorial depth in visual scenes and images. The present study investigates the conditions under which luminance or color either strengthens or overrides geometric depth cues. We investigated how luminance contrast associated with the color red and color contrast interact with relative height in the visual field, partial occlusion, and interposition to determine the probability that a given figure presented in a pair is perceived as "nearer" than the other. Latencies of "near" responses were analyzed to test for effects of attentional selection. Figures in a pair were supported by luminance contrast (Experiment 1) or isoluminant color contrast (Experiment 2) and combined with one of the three geometric cues. The results of Experiment 1 show that the luminance contrast of a color (here red), when it does not interact with other colors, produces the same effects as achromatic luminance contrasts. The probability of "near" increases with the luminance contrast of the color stimulus, the latencies for "near" responses decrease with increasing luminance contrast. Partial occlusion is found to be a strong enough pictorial cue to support a weaker red luminance contrast. Interposition cues lose out against cues of spatial position and partial occlusion. The results of Experiment 2, with isoluminant displays of varying color contrast, reveal that red color contrast on a light background supported by any of the three geometric cues wins over green or white supported by any of the three geometric cues. On a dark background, red color contrast supported by the interposition cue loses out against green or white color contrast supported by partial occlusion. These findings reveal that color is not an independent depth cue, but is strongly influenced by luminance contrast and stimulus geometry. Systematically shorter response latencies for stronger "near" percepts demonstrate that selective visual attention reliably detects the most likely depth cue combination in a given configuration.

Color Perception↗
PubMed1995

Measurement and modeling of depth cue combination: in defense of weak fusion.

Various visual cues provide information about depth and shape in a scene. When several of these cues are simultaneously available in a single location in the scene, the visual system attempts to combine them. In this paper, we discuss three key issues relevant to the experimental analysis of depth cue combination in human vision: cue promotion, dynamic weighting of cues, and robustness of cue combination. We review recent psychophysical studies of human depth cue combination in light of these issues. We organize the discussion and review as the development of a model of the depth cue combination process termed modified weak fusion (MWF). We relate the MWF framework to Bayesian theories of cue combination. We argue that the MWF model is consistent with previous experimental results and is a parsimonious summary of these results. While the MWF model is motivated by normative considerations, it is primarily intended to guide experimental analysis of depth cue combination in human vision. We describe experimental methods, analogous to perturbation analysis, that permit us to analyze depth cue combination in novel ways. In particular these methods allow us to investigate the key issues we have raised. We summarize recent experimental tests of the MWF framework that use these methods.

Bayes Theorem↗
PubMed2006

The spatio-temporal brain dynamics of processing and integrating sound localization cues in humans.

Interaural intensity and time differences (IID and ITD) are two binaural auditory cues for localizing sounds in space. This study investigated the spatio-temporal brain mechanisms for processing and integrating IID and ITD cues in humans. Auditory-evoked potentials were recorded, while subjects passively listened to noise bursts lateralized with IID, ITD or both cues simultaneously, as well as a more frequent centrally presented noise. In a separate psychophysical experiment, subjects actively discriminated lateralized from centrally presented stimuli. IID and ITD cues elicited different electric field topographies starting at approximately 75 ms post-stimulus onset, indicative of the engagement of distinct cortical networks. By contrast, no performance differences were observed between IID and ITD cues during the psychophysical experiment. Subjects did, however, respond significantly faster and more accurately when both cues were presented simultaneously. This performance facilitation exceeded predictions from probability summation, suggestive of interactions in neural processing of IID and ITD cues. Supra-additive neural response interactions as well as topographic modulations were indeed observed approximately 200 ms post-stimulus for the comparison of responses to the simultaneous presentation of both cues with the mean of those to separate IID and ITD cues. Source estimations revealed differential processing of IID and ITD cues initially within superior temporal cortices and also at later stages within temporo-parietal and inferior frontal cortices. Differences were principally in terms of hemispheric lateralization. The collective psychophysical and electrophysiological results support the hypothesis that IID and ITD cues are processed by distinct, but interacting, cortical networks that can in turn facilitate auditory localization.

Acoustic Stimulation↗
PubMed2006

The effect of rhythmic somatosensory cueing on gait in patients with Parkinson's disease.

BACKGROUND AND AIMS: Gait and gait related activities in patients with Parkinson's disease (PD) can be improved with rhythmic auditory cueing (e.g. a metronome). In the context of a large European study, a portable prototype cueing device was developed to provide an alternative for rhythmic auditory cueing: rhythmic somatosensory cueing (RSC, a miniature vibrating cylinder attached to the wrist). We investigated whether PD patients could adapt their walking pattern using RSC under conditions of changing walking speed and the presence of potentially distracting visual flow while walking on a treadmill. METHODS: A total of 17 patients with PD participated (mean age 63.4+/-10.3 years; Hoehn-Yahr score 2.5+/-0.9, mean Unified Parkinson's Disease Rating Scale score 49.8+/-13.7, mean disease duration 7.7+/-5.1 years). They performed systematic walking speed manipulations under 4 conditions in a random order: (1) no cue, no visual flow, (2) no cue, visual flow, (3) cue, no visual flow and (4) cue, visual flow. Visual flow in the form of a virtual corridor that moved at the current walking speed was projected on a 2 x 2 m rear-projection screen. The cueing rhythm was set at -10% of preferred stride frequency at each speed. Stride frequency was assessed using peaks in the trajectories of thigh sagittal plane segmental angles. RESULTS: Walking with RSC resulted in lower stride frequencies, and thus larger step lengths (p-values <0.05), regardless of walking speed. The presence of visual flow did not impair the use of RSC, as evidenced by the lack of differences between conditions 3 and 4 (p>0.05). CONCLUSION: Rhythmic somatosensory cueing may be a viable alternative for auditory cueing and is robust to changes in walking speed and visual distractors.

Aged↗
PubMed2005

Preference for cocaine- versus pup-associated cues differentially activates neurons expressing either Fos or cocaine- and amphetamine-regulated transcript in lactating, maternal rodents.

We studied the neuronal basis of the motivational response to two powerful but radically different rewards-cocaine and maternal nurturing of pups in the postpartum rat (dam) which is in a unique motivational state. We used a place preference method designed to offer a choice between cues associated with a natural reinforcer (pups) and those associated with a pharmacologic reinforcer (cocaine). Using c-Fos or cocaine- and amphetamine-regulated transcript (CART) immunocytochemistry, we identified the neuronal groups that are activated when the dams expressed a preference for either cues-associated with pups or cues-associated with cocaine. Dams that preferred the cocaine-associated cues had more c-Fos positive neurons in medial prefrontal cortex, nucleus accumbens, and basolateral nucleus of amygdala than pup-associated cue preferring dams or control. Except for the accumbens, there was activation of neurons in these same regions with the pup-associated cue preference. In the nucleus accumbens only CART-immunoreactive (not c-Fos) neurons were activated with pup-cue preference. Notably, the medial preoptic area was the single area where greater activation of neurons was seen with a preference for pup-associated versus cocaine-associated cues. These responses were identified in the absence of the stimuli (cocaine or pups) and are proposed to be, in part, activation of these neurons related to motivational processing. Neither the distribution of neurons responding to pup-associated cue preference nor the demonstration that CART-expressing neurons are responsive to reward-associated cue preference has been previously reported. We hypothesize that the expression of preference for cocaine versus pup-associated cues is made possible by the concerted activity of these regionally distributed networks of neurons that are in part specific to the preference response.

Animals↗
PubMed2005

The modulatory effects of nicotine on parietal cortex activity in a cued target detection task depend on cue reliability.

This functional magnetic resonance imaging study investigates the effects of nicotine in a cued target detection task when changing cue reliability. Fifteen non-smoking volunteers were studied under placebo and nicotine (Nicorette polacrilex gum 1 and 2 mg). Validly and invalidly cued trials were arranged in blocks with high, middle and low cue reliability. Two effects of nicotine were investigated: its influence on i) parietal cortex activity underlying the processing of invalid vs. valid trials (i.e. validity effect) and ii) neural activity in the context of low, middle and high informative value of the cue (i.e. cue reliability effect). Nicotine did not affect behavioral performance. However, nicotine reduced the difference in the blood oxygenation level dependent (BOLD) signal between invalid and valid trials in the right intraparietal sulcus. The reduction of parietal activity in invalid trials was smaller in the low cue reliability condition. The same posterior parietal region exhibited a nicotinic modulation of BOLD activity in valid trials which was dependent on cue reliability: Nicotine specifically enhanced the neural activity during valid trials in the context of low cue reliability, i.e. when subjects are already in a state of low certainty. We speculate that the right intraparietal sulcus might be part of two networks working in parallel: one responsible for reorienting attention and the other for the cholinergic modulation of cue reliability. By reducing the use of the cue, nicotine modulates parietal activity related to reorienting attention in conditions with higher cue certainty. On the other hand, nicotine increases parietal activity in states of low certainty. This enhanced activation might influence brain regions, such as the posterior cingulate, directly involved in the processing of cue reliability.

Adult↗
PubMed2006

Motor activity (exploration) and formation of home bases in mice (C57BL/6) influenced by visual and tactile cues: modification of movement distribution, distance, location, and speed.

The motor activity of mice in tests of "exploration" is organized. Mice establish home bases, operationally defined as places where they spend long periods of time, near physical objects and nesting material from which they make excursions. This organization raises the question of the extent to which mouse motoric activity is modulated by innate predispositions versus environmental influences. Here the influence of contextual cues (visual and tactile) on the motor activity of C57BL/6 mice was examined: (1) on an open field that had no walls, a partial wall, or a complete wall, (2) in the presence of distinct visual cues, room cues, or in the absence of visual cues (infrared light), and (3) in the presence of configurations of visual and tactile cues. Mice were generally less active in the presence of salient cues and formed home bases near those cues. In addition, movement speed, path distribution, and the number and length of stops were modulated by contextual cues. With repeated tests, mice favored tactile cues over visual cues as their home base locations. Although responses to cues were robust over test days, conditioning to context was generally weak. That the exploratory behavior of mice is affected by experience and context provides insights into performance variability and may prove useful in investigating the genetic and neural influences on mouse behavior.

Animals↗
PubMed1999

Facilitation and inhibition arising from the exogenous orienting of covert attention depends on the temporal properties of spatial cues and targets.

On the covert orienting of visual attention task (COVAT), responses to targets appearing at the location indicated by a non-predictive spatial cue are faster than responses to targets appearing at uncued locations when stimulus onset asynchrony (SOA) is less than approximately 200 ms. For longer SOAs, this pattern reverses and RTs to targets appearing at uncued locations become faster than RTs to targets appearing at the cued location. This facilitation followed by inhibition has been termed the biphasic effect of non-predictive peripheral spatial cues. Currently, there is debate about whether these two processes are independent. This issue was addressed in a series of experiments where the temporal overlap between the peripheral cue and target was manipulated at both short and long SOAs. Results showed that facilitation was present only when the SOA was short and there was temporal overlap between cue and target. Conversely, inhibition occurred only when the SOA was long and there was no temporal overlap between cue and target. The biphasic effect, with an early facilitation followed by a later inhibition, occurred only when the cue duration was fixed such that there was temporal overlap between the cue and target at short but not long SOAs. In a final experiment, the duration of targets the temporal overlap between cue and target and the SOA were manipulated factorially. The results showed that facilitation occurred only when the SOA was short, there was temporal overlap between cue and target and the target remained visible until the subject responded. These results suggest that the facilitation and inhibition found on COVATs which use non-informative peripheral cues are independent processes and their presence and magnitude is related to the temporal properties of cues and targets.

Adult↗
PubMed2004

The time course of the effects of central and peripheral cues on visual processing: an event-related potentials study.

OBJECTIVE: The varying results of visual event-related potential (ERP) studies of central and peripheral cueing suggest that these types of cue may modulate stimuli processing with different time courses. The aim of this study was to investigate differences in the time course of facilitatory effects on the visual processing induced by peripheral and central cues. METHODS: ERPs were recorded for visual target stimuli that were preceded by informative-central, informative-peripheral or uninformative-peripheral cues with stimulus onset asynchronies (SOAs) of 100, 300, 500 or 700 ms. RESULTS: Validly cued stimuli elicited an enhanced P1 component with peripheral cueing at 100 ms SOA. P1 amplitude in valid trials was reduced at 300, 500 and 700 ms SOAs with uninformative-peripheral cueing, but only at 500 ms SOA with informative-peripheral cueing. With informative-central cueing, there was no validity effect on P1. CONCLUSIONS: These results suggest that the automatic attraction of attention by a peripheral cue results in improved sensory processing at the cued location. This facilitation is replaced by an inhibitory effect when SOA increases, although cue informativeness may modulate this effect. Central cueing does not affect sensory processing at the P1 level.

Adult↗
PubMed2001

Disengaging attention: on the locus of the cue-duration effect in partial report.

Increasing cue duration impairs performance in bar-probe partial report when cues are presented peripherally, but not centrally (P. Dixon, R. Gordon, A. Leung, & V. Di Lollo, 1997). Three experiments examined whether this cue-duration effect reflects processes of exogenous attention. The effect of cue duration on partial report performance with peripheral, but not central, cues was replicated (Experiment 1). Further experiments manipulated the degree that exogenous versus endogenous modes of selection were favored and found that the cue-duration effect for peripheral cues was reduced (a) when blocks contained a high proportion of central cues (Experiment 2) and (b) when the color of the cue indicated the location of the target (Experiment 3). These findings challenge the view that the cue-duration effect is restricted to exogenous attention and are discussed in terms of the process of disengaging attention from the cue to reallocate attention to the target representation.

Attention↗
PubMed2006

Interpreting instructional cues in task switching procedures: the role of mediator retrieval.

In 3 experiments the role of mediators in task switching with transparent and nontransparent cues was examined. Subjects switched between magnitude (greater or less than 5) and parity (odd or even) judgments of single digits. A cue-target congruency effect indicated mediator use: subjects responded faster to congruent cue-target combinations (e.g., ODD-3) than to incongruent cue-target combinations (e.g., ODD-4). Experiment 1 revealed significant congruency effects with transparent word cues (ODD, EVEN, HIGH, and LOW) and with relatively transparent letter cues (O, E, H, and L) but not with nontransparent letter cues (D, V, G, and W). Experiment 2 revealed significant congruency effects after subjects who were trained with nontransparent letter cues were informed of the relations between cues and word mediators halfway through the experiment. Experiment 3 showed that congruency effects with relatively transparent letter cues diminished over 10 sessions of practice, suggesting that subjects used mediators less as practice progressed. The results are discussed in terms of the role of mediators in interpreting instructional cues.

Analysis of Variance↗
PubMed2002

The influence of cue-task association and location on switch cost and alternating-switch cost.

Task-switching performance is strongly influenced by whether the imperative stimulus uniquely specifies which task to perform: Switch cost is substantial with bivalent stimuli but is greatly reduced with univalent stimuli, suggesting that available contextual information influences processing in task-switching situations. The present study examined whether task-relevant information provided by task cues influences the magnitude of switch cost in a parallel manner. Cues presented 500 ms prior to a trivalent stimulus indicated which of three tasks to perform. These cues either had a preexisting association with the to-be-performed task (verbal cues), or a recently learned association with the task (spatial and shape cues). The results paralleled the effects of stimulus bivalence: substantial switch cost with recently learned cue-task associations and greatly reduced switch cost with preexisting cue-task associations. This suggests that both stimulus-based and cue-based information can activate the relevant task set, possibly providing external support to endogenous control processes. Alternating-switch cost, a greater cost for switching back to a recently abandoned task, was also observed with both preexisting and recently learned cue-task associations, but only when all tasks were presented in a consistent spatial location. When spatial location was used to cue the to-be-performed tasks, no alternating-switch cost was observed, suggesting that different processes may be involved when tasks are uniquely located in space. Specification of the nature of these processes may prove to be complex, as post-hoc inspection of the data suggested that for the spatial cue condition, the alternating-switch cost may oscillate between cost and benefit, depending on the relevant task.

Adolescent↗
PubMed2001

Effects of linguistic cues and stimulus cohesion on intelligibility of severely dysarthric speech.

This study examined the effects of supplemental cues on the intelligibility of unrelated sentences and related sentences (narratives) produced by 4 women with severe dysarthria secondary to cerebral palsy. Visual images containing alphabet, topic, combined (alphabet and topic together), and no cues were imposed in real time on audio speech samples and presented to 72 nondisabled listeners. Statistical results showed that cue conditions had similar effects on unrelated and on related sentence intelligibility. Combined cues resulted in higher intelligibility scores than any other cue condition, no cues resulted in lower intelligibility scores than any other cue condition, and alphabet cues yielded higher intelligibility scores than topic cues. Intelligibility of related and unrelated sentences differed only for alphabet cues where related sentences had greater intelligibility than unrelated sentences. Results are discussed relative to the quantity and type of cues.

Adult↗
PubMed2002

Surface-illuminant ambiguity and color constancy: effects of scene complexity and depth cues.

Two experiments were conducted to study how scene complexity and cues to depth affect human color constancy. Specifically, two levels of scene complexity were compared. The low-complexity scene contained two walls with the same surface reflectance and a test patch which provided no information about the illuminant. In addition to the surfaces visible in the low-complexity scene, the high-complexity scene contained two rectangular solid objects and 24 paper samples with diverse surface reflectances. Observers viewed illuminated objects in an experimental chamber and adjusted the test patch until it appeared achromatic. Achromatic settings made tinder two different illuminants were used to compute an index that quantified the degree of constancy. Two experiments were conducted: one in which observers viewed the stimuli directly, and one in which they viewed the scenes through an optical system that reduced cues to depth. In each experiment, constancy was assessed for two conditions. In the valid-cue condition, many cues provided valid information about the illuminant change. In the invalid-cue condition, some image cues provided invalid information. Four broad conclusions are drawn from the data: (a) constancy is generally better in the valid-cue condition than in the invalid-cue condition: (b) for the stimulus configuration used, increasing image complexity has little effect in the valid-cue condition but leads to increased constancy in the invalid-cue condition; (c) for the stimulus configuration used, reducing cues to depth has little effect for either constancy condition: and (d) there is moderate individual variation in the degree of constancy exhibited, particularly in the degree to which the complexity manipulation affects performance.

Adult↗
PubMed2006

Effects of motion parallax and perspective cues on perceived size and distance.

In three experiments we examined the relative effectiveness of motion parallax and two perspective cues for the perception of size and distance. The experimental stimuli consisted of two ellipses (a standard and a comparison) and a horizontal line that indicated the horizon. The subject's task was to report the apparent size and distance of the comparison stimulus relative to the standard stimulus. Two perspective cues were given by the relative heights of the two stimuli and the absolute height of the standard stimulus below the horizon. Motion parallax was defined by both the ratio and the difference in angular velocities between the two stimuli on the display. In experiment 1 we examined the effects of the two perspective cues and the motion parallax. In experiment 2 we eliminated the horizon line, and examined the role of the horizon in size and distance perception. In experiment 3 we separately evaluated the effects of motion parallax and the relative height cues. The results from the three experiments showed that the effect of motion parallax and the two perspective cues were different in three ways. First, the relative effectiveness of motion parallax and the two perspective cues differed for size and distance estimates. For size estimates, the motion parallax was more effective than the perspective cues (experiments 1 and 3). For distance estimates, the motion parallax was as effective as the two perspective cues (experiments 1 and 3). Second, the role of the horizon differed for size and distance estimates. The size estimates were strongly affected by the horizon, while the distance estimates were not affected much by the horizon (experiment 2). Third, the effective perspective cues differed for the size estimates and the distance estimates: size estimates were affected by the perspective cues as a combination of the horizon and relative height; distance estimates were affected by the perspective cues as an interaction between the absolute and relative heights without the horizon line.

Cues↗