Psychology
Visual Cues and Constancies
Visual cues refer to the information that our visual system uses to perceive depth, distance, and size. Visual constancies are the brain's ability to perceive objects as maintaining their size, shape, and color despite changes in the viewing angle or lighting conditions. These cues and constancies play a crucial role in our perception of the visual world.
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11 Key excerpts on "Visual Cues and Constancies"
eBook - PDFHandbook of Perception and Action
Perception
- Wolfgang Prinz, Bruce Bridgeman(Authors)
- 1996(Publication Date)
- Academic Press(Publisher)
Part II Perception of Objects, Events and Actions This Page Intentionally Left Blank Chapter 7 Perceptual Constancies: Analysis and Synthesis Wayne L. Shebilske and Aaron L. Peters Texas A&M University 1 INTRODUCTION Perceptual constancies are tendencies for the appearances of objects to remain unaltered as their sensory correlates vary. Day and McKenzie (1977, p. 291) distinguish two kinds: (1) egocentric constancies, which 'refer to constancy of an object's apparent position in space in relation to the observer as the sensory representation of that position varies'; and (2) object constancies, which 'refer mainly to constancy of object properties as their sensory images vary'. Woodworth (1938, p. 595) described visual constancies as follows: '... the retinal image continually changes without much changing the appearance of objects. The apparent size of a person does not change as he moves away from you. A ring turned at various angles to the line of sight, and therefore projected as a varying ellipse on the retina, continues to appear circular. Part of a wall, standing in shadow, is seen as the same color as the well-lighted portion. Still more radical are the changes in the retinal image that occur when we move about a room and examine its contents from various angles. In spite of the visual flux the objects seem to remain in the same place.' Similar constancies exist in other sensory modalities, such as constancies for loudness as a function of distance (Mershon et al., 1981) and odor (we tend to perceive the same olfactory intensity whether we take a shallow or deep sniff, despite changes of the amount of stimulus reaching the olfactory receptors (Teght- soonian et al., 1978)). Most constancy research, however, has been done on visual constancies, such as constancies of distance (Hill, 1972; Purdy and Gibson, 1955), color (Graham, 1965), position and direction (Shebilske, 1977) and motion (Richards, 1977).
eBook - ePubPerceptual Development in Early Infancy
Problems & Issues
- B. McKenzie, R. H. Day, B. McKenzie, R. H. Day(Authors)
- 2013(Publication Date)
- Psychology Press(Publisher)
It is helpful first to consider briefly the history of the study of size constancy and the situations in which it was first studied. Since size constancy in infancy must necessarily involve a capacity to discriminate object size, evidence for this capacity will also be considered before turning to size constancy itself. Distance discrimination, which is also involved in size constancy is discussed later in the paper.Visual Size Constancy
The relative constancy of visually perceived size with variation in the size of the retinal projection due to changes in distance was the first of the perceptual constancies to be recognized and to receive serious scientific attention. Berkeley (1969 ) mentioned it in his A New Theory of Vision in 1734 and attributed it to simultaneous perception of object distance, a view which still has currency (see Boring, 1942 ). Fechner in 1860 quantified the effect in the near field of vision by matching the apparent separation between one pair of compass points at one distance with the apparent separation between a second pair at another distance. Early systematic studies of size constancy were conducted by Martius (1889 ) using vertical rods placed at different distances and by Hillebrand (1902 ) using frontoparallel extents between a “corridor” of hanging threads, an arrangement that came to be called the vista or alley effect. Later, Thouless (1931 ) and Brunswik (1933 ) recognized visual size constancy as one of a class of effects which they investigated and compared by means of an appropriate common index. Thouless (1931 ) referred to perceptual constancy as “phenomenal regression to the real object” thus characterizing it as a shift of the perceived property away from its retinal representation towards the physical or “real” state of affairs.Visual Size Constancy in Adulthood
For an adult observer viewing under “normal” conditions—binocular vision with unrestricted eye and head movements in a setting rich in texture, pattern and objects—overconstancy of size is usual (Gilinsky, 1955 ; Holway & Boring, 1941 ; Wohlwill, 1963a , 1963b ). This “overshoot” effect occurs for objects as far away as about 1200 m (Gilinsky, 1955 ). The degree of overconstancy varies according to the instructions to the observer, the availability of information or “cues” to distance, and experimental procedures. Carlson (1960 , 1962
eBook - ePubPerception
Theory, Development and Organisation
- Paul Rookes, Jane Willson(Authors)
- 2005(Publication Date)
- Routledge(Publisher)
- Gestalt laws are rather vague and are sometimes difficult to distinguish one from another. The basic law of simplicity is quite hard to define and the simplest interpretation of an ambiguous figure is not always easy to predict.
- Many of the illustrations of organisation apply to very simple stimuli. Complex scenes involving everyday perception do not easily fit into a model based on simple two-dimensional illustrations.
- Eysenck and Keane (1995) suggest that the processes proposed by the Gestalt psychologists probably account only for the early stages of perceptual processing which will be organised later by previous experience.
Perceptual constancies
Constancy is the tendency for qualities of objects to stay the same despite changes in the way we view them. This is an important facet of visual perception. Try to imagine what it would be like if our perceptions were based purely on the image falling on the retina (the proximal stimulus). As you walked along the road towards a post box, it would appear to grow larger. As you moved your arm, your round wrist-watch would appear to change into an elliptical shape. As you moved from natural sunlight outdoors into artificial light indoors, your white shirt would appear yellow. Fortunately for us, our perceptual system seems to ensure that, in most circumstances our distal stimulus (our perceptual experience of objects ‘out there’) remains the same regardless of changes in the proximal stimulus.Size constancy
This is our ability to see objects as remaining more or less the same size as we move closer or further away. The proximal size of an object can shrink and expand, but the distal size of the object seems to stay about the same. If a 6 ft. man walks away from you, you continue to perceive him as man-sized, regardless of his distance from you. It is interesting that this ability to maintain size constancy disappears under certain circumstances. When we look down from a plane, for example, cars and houses really do look like miniatures. When we take a holiday photo of a glorious, panoramic view, we can be quite disappointed with the result. In the photo, those majestic mountains can look quite pathetic. The camera, unlike the human perceiver, only registers angular size and does not compensate for the size changes that are related to distance changes. Our own size constancy mechanism does not appear to work as well when we view pictures as compared to real objects.
eBook - PDFCognitive Psychology
A Student's Handbook
- Michael W. Eysenck, Mark T. Keane(Authors)
- 2020(Publication Date)
- Psychology Press(Publisher)
Most models focus on the accuracy of depth-perception judgements. However, there are circum- stances (e.g., presence of a fierce wild animal) where rapid if somewhat inaccurate judgements are preferable. More generally, humans focus on “computational efficiency” – our goal is to maximise reward while min- imising the computational costs of visual processing (Summerfield & Li, 2018). Thus, optimality of depth-perception judgements does not depend solely on performance accuracy. Size constancy Size constancy is the tendency for any given object to appear the same size whether its size in the retinal image is large or small. For example, if KEY TERM Size constancy Objects are perceived to have a given size regardless of the size of the retinal image. 78 Visual perception and attention someone walks towards you, their retinal image increases progressively but their apparent size remains the same. Why do we show size constancy? Many factors are involved. An object’s apparent distance is especially important when judging its size. For example, an object may be judged to be large even though its retinal image is very small provided it is far away. According to the size-distance invari- ance hypothesis (Kilpatrick & Ittelson, 1953), perceived size is proportional to perceived distance. Findings Haber and Levin (2001) argued that an object’s perceived size depends on memory of its familiar size as well as perceptual information concerning its distance. Initially, observers estimated the sizes of common objects with great accuracy from memory. Then they saw various objects at close (0–50 metres) or distant (50–100 metres) viewing range and made size judgements. Some familiar objects were almost invariant in size (e.g., bicycle) or of varying size (e.g., television set); there were also unfamiliar stimuli (e.g., ovals).
eBook - ePub- Mark Wagner(Author)
- 2012(Publication Date)
- Psychology Press(Publisher)
projective instructions attempt to incline the observer to report the perceived visual angle that a standard subtends. Usually this is done by referencing an analogy such asking the subject to pretend that their visual experience is painted onto a two-dimensional canvas and that they should adjust the comparison so that it takes up as much of the visual canvas as the standard. In other words, the observer is encouraged to take an artist’s-eye view.Depth cue availability. Stimulus cue conditions vary from rich naturalistic conditions with plenty of cues to depth available such as a grassy field or a hall with many scattered objects intervening between the observer and the target, to controlled laboratory settings with uniform surface conditions, viewing through artificial pupils, partially or totally darkened rooms with only the standard and comparison stimuli illuminated, and viewing stimuli against dark backgrounds through a darkened tunnel. Here, for example, the grassy field would be considered a highly full-cue condition, and the darkened tunnel would produce a very reduced-cue setting. Experiments also vary between binocular and monocular viewing conditions, with monocular viewing being considered as a reduced-cue setting.Historical ReviewAccording to Ross and Plug (1998), interest in the problem of size constancy dates back to ancient times. Ptolemy described the phenomenon in the second century A.D., as did Malebranche in the 17th century. Outlines of the basic theoretical explanations currently employed by modern researchers can also be traced to antiquity. Explanations based on the Size-Distance Invariance Hypothesis were proposed by Euclid (c. 300 B.C.), Iby al-Haytham (c. 1030), DesCartes (1637), and Helmholtz (1867, 1881). Relative-size related explanations were laid out by Plotinus (c. 300 A.D.), Leonardo da Vinci (c. 1500), and Hering in the 19th century.The first modern experimental investigation of the topic may be attributed to Martius (1889). Using apparent size instructions, Martius asked observers to match a near standard rod by choosing among a set of distant comparison rods. He found that his subjects generally produced accurate matches at all distances, with a slight tendency toward underconstancy.
eBook - PDFPerceptual Illusions
Philosophical and Psychological Essays
- C. Calabi(Author)
- 2017(Publication Date)
- Palgrave Macmillan(Publisher)
In particular, we can recognize that there is not just one type of constancy, but two. In addition, I aim to show how a proper understanding of the constancies throws light on another issue: illusions are wrongly thought of as simply opposed to the veridical. They show how, in perception, error and truth can be inter-twined. 5 Perceptual Constancies: Illusions and Veridicality Barry Maund 88 Barry Maund (The approach I am taking, to the constancies and to veridicality, com- plements the approach that Robert Schwartz takes to illusions in “The Illusion of Visual Illusions” – this volume. Each of us finds puzzles in the way that the respective phenomena are described.) 1 1. Two ways of characterizing the perceptual constancies Stephen Palmer expresses one way of describing the perceptual constan- cies, when, in his book Vision Science: From Photons to Phenomenology , he states that “the fact that people veridically perceive the constant, unchanging properties of external objects rather than the more tran- sient properties of their retinal images is called perceptual constancy” (Palmer, 1999, 312). This description, which stresses the link between perceptual constancy and veridical perception, is common. (See R. O. Brown, 2003, 252; J. Hochberg, 1988, and E. B. Goldstein, 2002, 250–1.) The philosopher, Sean Kelly, provides a fuller description, with illustra- tive examples: A common example of perceptual constancy is found in the fact that there are many different viewpoints from which I see a table as square, for instance, even though the image projected from the table onto my retina from each of these perspectives is different, and in fact is rarely itself a square image ... . Likewise in the case of size constancy, a man continues to look the same size as he walks away from me, even though the size of the image his body casts onto my retina decreases with distance.
eBook - ePub- M.D. Vernon(Author)
- 2017(Publication Date)
- Routledge(Publisher)
The Constancies(1) Introduction
A form of interaction between ‘figure’ and ‘ground’ in perception which has given rise to continued speculation and an enormous amount of experimental investigation is that which occurs in the so-called ‘constancies’. It appears that an object may retain the shape, size and colour which are characteristically associated with its identity although the information as to these qualities which is projected to the eye varies with variation in the relation of the object to its surroundings. We noted in Chapter II that infants learnt to identify objects and to disregard changes in the sensory data related to shape which occur when the objects are tilted or rotated; and changes in projected size which are produced by varying the distance of the object from the eye. So also it is found that from an early age children and adults may seem actually to perceive a rotated shape as having the same form as that of the unrotated shape; or perceive a form part-way between that of the unrotated shape and that of the actually projected shape. And they may perceive the size of a distant object to approximate to the size of the same object when it is close to them. Finally, they may perceive the brightness and colour to vary less than do the brightness and colour of the projected image. But the preservation of perceived constancy in spite of variation in the projected sensory data depends to a large extent on the ability of the observer to differentiate the inherent qualities of the object from those aspects which vary with changes in the environmental setting. Thus in general it is necessary for the observer to perceive the characteristics of the environmental setting or ‘ground’ clearly and unambiguously.These phenomena were first described independently by Thouless (1931a and 1931b) and by the Gestalt psychologists, notably Koffka (1935). The former termed them ‘phenomenal regression to the real object’, and the latter, the ‘constancies
eBook - PDFPsychology
Modules for Active Learning
- Dennis Coon, John Mitterer, Tanya Martini, , Dennis Coon, John Mitterer, Tanya Martini, (Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
To perceive your hand accurately, you had to draw on past experience to provide a top-down plan for con-structing your perception. Some of these plans are so ba-sic that they seem native , or inborn. An example is the ability to see a line on a piece of paper. Likewise, even newborn babies show some evidence of size constancy (Granrud, 2006). However, many of our perceptions are empirical , or based on prior experience. For instance, cars, houses, and people look like toys when seen from a great distance or from an unfamiliar perspective, such as from the top of a skyscraper. This suggests that although some size constancy is innate, it also is affected by learn-ing (Granrud, 2009). In shape constancy , the shape of an object remains stable, even though the shape of its retinal image changes. You can demonstrate shape constancy by looking at this page from di-rectly overhead and then from an angle. Obviously, the page is rectangular, but most of the images that reach your eyes are distorted. Yet though the book’s image changes, your percep-tion of its shape remains constant (for additional examples, see ➤ Figure 20.9 ). On the highway, alcohol intoxication impairs size and shape constancy, adding to the accident rate among drunk drivers (Goldstein & Brockmole, 2017). Let’s say that you are outside in bright sunlight. Beside you, a friend is wearing a gray skirt and a white blouse. Suddenly a cloud shades the sun. It might seem that the blouse would grow dimmer, but it still appears to be bright white. This happens because the blouse continues to reflect a greater proportion of light than nearby objects. Bright-ness constancy refers to the fact that the relative bright-ness of objects appears to stay the same as lighting condi-tions change. However, this holds true only if the blouse and other objects are all illuminated by the same amount of light.
- E. Chekaluk, K.R. Llewellyn(Authors)
- 1992(Publication Date)
- North Holland(Publisher)
In this chapter, we will attempt to show how all three of these paradoxes may be resolved parsimoniously on the basis of a single coherent theoretical account that incorporates the two hypotheses mentioned above as adjuncts to Robinson’s closed-loop model of the oculomotor system. Understandably, we will be turning our attention to a careful consideration of Robinson’s model. But first, some general introductory remarks about the perception of visual direction. Visual Direction Constancy 3 3. Viiual Direction Constancy Typically, the visible environment does not appear to move when we rotate our eyes, even though eye rotations sweep our retinas across the optic array. That is, in spite of the motion of the proximal stimulus across the retina, the distal environment appears to be undisturbed or to remain stable. The distal environment is said to remain stable, as if it were in fact motionless. But, of course, our terrestrial environment is not motionless. It is moving at a very high velocity through the solar system as the earth orbits the sun and spins on its axis. Stability is in the eye of the beholder. Or, more exactly, motion is always relative to a frame of reference. When we take our environment to be motionless we are in fact imposing a particular frame of reference, namely, the surface of the earth. To say that the distal environment remains stable in spite of eye movements is to say that the visible environment does not appear to move relative to the surface of the earth when we shift our gaze. The perceptual phenomenon known as visual space constancy merely reflects our constant utitlization of the surface of the earth as an allocentric frame of reference; it does not imply that the earth is immobile. Our utilization of the surface of the earth as a perceptual frame of reference is, at once, eminently reasonable and difficult to understand.
eBook - PDF- E. Goldstein, James Brockmole(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
The following dem- onstration illustrates size constancy in another way. DEMONSTRATION Perceiving Size at a Distance Hold a quarter between the fingertips of each hand so you can see the faces of both coins. Hold one coin about a foot from you and the other at arm’s length. Observe the coins with both of your eyes open and note their sizes. Under these conditions, most people perceive the near and far coins as being approxi- mately the same size. Now close one eye, and holding the coins so they appear side-by-side, notice how your perception of the size of the far coin changes so that it now appears smaller than the near coin. This demonstrates how size constancy is decreased under conditions of poor depth information. Although students often propose that size constancy works because we are familiar with the sizes of objects, research has shown that observers can accurately estimate the sizes of unfamiliar objects viewed at different distances (Haber & Levin, 2001). Size Constancy as a Calculation The link between size constancy and depth perception has led to the proposal that size constancy is based on a mechanism called size– distance scaling that takes an object’s distance into account (Gregory, 1966). Size–distance scaling operates according to the equation S 5 K(R 3 D) where S is the object’s perceived size, K is a constant, R is the size of the retinal image, and D is the perceived distance of the object. (Since we are mainly interested in R and D, and K is a scaling factor that is always the same, we will omit K in the rest of our discussion). According to the size–distance equation, as a person walks away from you, the size of the person’s image on your retina (R) gets smaller, but your perception of the person’s distance (D) gets larger. These two changes balance each other, and the net result is that you perceive the person’s size (S) as staying the same.
eBook - PDFSensation, Perception and Action
An Evolutionary Perspective
- Johannes Zanker(Author)
- 2010(Publication Date)
- Bloomsbury Academic(Publisher)
54 1 OVERVIEW We are living in a world with three spatial dimensions and an additional temporal dimension – but the eyes provide us with flat (2D) images. A single, static image, like a painting or photograph, contains a plethora of information, and humans have highly developed processing mechanisms to extract such information. Brightness and colour per-ception, shape perception and object recognition can operate to a large extent on the basis of static 2D representations. Adding depth information, however, has vital relevance for organising behaviour, because we operate in a dangerous 3D environment, and any pred-ecessor in our evolution misjudging the distance of a branch in the canopy of the jungle, or being unaware of the abyss at a cliff, would have little chance to let us inherit genes that would determine such fallible depth perception. Our survey of visual depth information starts with pictorial cues: perspective, texture, contrast, size, occlusion; then moves on to binocular cues: signals generated by the movement of the eyes (vergence, accommodation) and by the different viewpoints of the two eyes (stereopsis); and finally describes dynami-cal cues (motion parallax), which is similar in its geometry to stereo, but very powerful at long distance. The range of possible depth cues and the range of processing mechanisms that are available to the human observer is discussed in relation to operating constraints (such as critical range), deficiencies (e.g. stereo-blindness) and applications (magic eye, 3D, IMAX ® ). A number of depth and size illusions, and their possible explanations, concludes this chapter: constancy scaling, Ponzo illusion, Ames room, hollow face illusion. THE THIRD DIMENSION OF THE WORLD – DEPTH PERCEPTION The world around us has four dimensions, three in space, and one in time.
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