Overflow, first-sight, and vanishing point distances in visual imagery

The relationship between the size of a familiar object and the distances at which it is imaged is examined in three experiments. The distance at which an imaged object overflows the visual field is linearly related to object size, a result consistent with the size-distance invariance hypothesis (Kosslyn, 1980). The distance at which an object is initially imaged, first-sight distance, is related to the object size by a power function with an exponent less than 1. In addition, time required to scan from the first-sight to the overflow distance increases as a function of the difference between the two distance estimates. The distance at which an imaged object becomes too small to be identified, vanishing point distance, is related to object size by a power function with an exponent less than 1. This result does not support predictions made from the size-distance invariance hypothesis or Kosslyn's model of visual imagery. Implications for a theory of visual imagery and memory are discussed.     

Memory psychophysics for visual area and length

Independent groups of observers made magnitude estimates of geographical area or interstate distance. In Experiment 1, observers estimated the areas of nations or of states of the United States from memory. In Experiment 2, estimates of state area were made either with a map present or from memory after the map had been studied. Similarly, in Experiment 3, observers made perceptual or memorial estimates of interstate distances. Perceptual estimates of distance and geographical area were related to actual stimulus magnitude by power functions whose exponents were similar to those found with conventional procedures. Memory estimates were also related to actual area and distance by power functions. Comparison of memory and perceptual exponents showed that for both area and distance, the memory exponent was equal to the square of the perceptual exponent. The results of Experiment 3 were predicted by a “re-perceptual” model of memory for continuous dimensions, which was developed to describe the results of Experiment 2.     

The effects of size,clutter, and complexity on vanishing-point distances in visual imagery

Summary The portrayal of vanishing-point distances in visual imagery was examined in six experiments. In all experiments, subjects formed visual images of squares, and the squares were to be oriented orthogonally to subjects' line of sight. The squares differed in their level of surface complexity, and were either undivided, divided into 4 equally sized smaller squares, or divided into 16 equally sized smaller squares. Squares also differed in stated referent size, and ranged from 3 in. to 128 ft along each side. After subjects had formed an image of a specified square, they transformed their image so that the square was portrayed to move away from them. Eventually, the imaged square was portrayed to be so far away that if it were any further away, it could not be identified. Subjects estimated the distance to the square that was portrayed in their image at that time, the vanishing-point distance, and the relationship between stated referent size and imaged vanishing-point distance was best described by a power function with an exponent less than 1. In general, there were trends for exponents (slopes on log axes) to increase slightly and for multiplicative constants (y intercepts on log axes) to decrease as surface complexity increased. No differences in exponents or in multiplicative constants were found when the vanishing-point was approached from either sub-threshold or suprathreshold directions. When clutter in the form of additional imaged objects located to either side of the primary imaged object was added to the image, the exponent of the vanishing-point function increased slightly and the multiplicative constant decreased. The success of a power function (and the failure of the size-distance invariance hypothesis) in describing the vanishing-point distance function calls into question the notions (a) that a constant grain size exists in the, imaginal visual field at a given location and (b) that grain size specifies a lower limit in the storage of information in visual images.     

Visual angle as a determinant of perceived interobject distance

Two new experiments and a reanalysis of Toye’s (1986)data are used to examine the relationship between true distance and perceived distance in natural scenes. In the first experiment, 8 subjects estimated 78 interobject distances, formed by all pairs of 13 objects, while viewing the objects from a fixed position. The results showed that estimated distance is a linear function of the visual angle between objects as well as of the true distance. This relationship results in distances perpendicular to the line of sight being overestimated in relation to true distances and to distances parallel to the line of sight. These findings were confirmed by reanalysis of a comparable data set from Toye. Since changes in the visual angle can come about through changes in alignment with the line of sight, viewing distance, or interobject distance, Experiment 2 was designed to determine whether the visual angle effect was due to one of these, or whether it was an independent effect. In Experiment 2, 8 subjects estimated six interobject distances from 12 viewing positions. The results showed that visual angle predicted estimated distance independently of how the change in visual angle came about, suggesting that the greater the visual angle between objects, the more their separation is overestimated.     

Mood-dependent retrieval in visual long-term memory: dissociable effects on retrieval probability and mnemonic precision

Although memories are more retrievable if observers’ emotional states are consistent between encoding and retrieval, it is unclear whether the consistency of emotional states increases the likelihood of successful memory retrieval, the precision of retrieved memories, or both. The present study tested visual long-term memory for everyday objects while consistent or inconsistent emotional contexts between encoding and retrieval were induced using background grey-scale images from the International Affective Picture System (IAPS). In the study phase, participants remembered colours of sequentially presented objects in a negative (Experiment 1a) or positive (Experiment 2a) context. In the test phase, participants estimated the colours of previously studied objects in either negative versus neutral (Experiment 1a) or positive versus neutral (Experiment 2a) contexts. Note, IAPS images in the test phase were always visually different from those initially paired with the studied objects. We found that reinstating negative context and positive context at retrieval resulted in better mnemonic precision and a higher probability of successful retrieval, respectively. Critically, these effects could not be attributed to a negative or positive context at retrieval alone (Experiments 1b and 2b). Together, these findings demonstrated dissociable effects of emotion on the quantitative and qualitative aspects of visual long-term memory retrieval.     

Reduced visual acuity is mirrored in low vision imagery

Research has examined the nature of visual imagery in normally sighted and blind subjects, but not in those with low vision. Findings with normally sighted subjects suggest that imagery involves primary visual areas of the brain. Since the plasticity of visual cortex appears to be limited in adulthood, we might expect imagery of those with adult-onset low vision to be relatively unaffected by these losses. But if visual imagery is based on recent and current experience, we would expect images of those with low vision to share some properties of impaired visual perception. We examined key parameters of mental images reported by normally sighted subjects, compared to those with early- and late-onset low vision, and with a group of subjects with restricted visual fields using an imagery questionnaire. We found evidence that those with reduced visual acuity report the imagery distances of objects to be closer than those with normal acuity and also depict objects in imagery with lower resolution than those with normal visual acuity. We also found that all low vision groups, like the normally sighted, image objects at a substantially greater distance than when asked to place them at a distance that ‘just fits’ their imagery field (overflow distance). All low vision groups, like the normally sighted, showed evidence of a limited visual field for imagery, but our group with restricted visual fields did not differ from the other groups in this respect. We conclude that imagery of those with low vision is similar to that of those with normal vision in being dependent on the size of objects or features being imaged, but that it also reflects their reduced visual acuity. We found no evidence for a dependence on imagery of age of onset or number of years of vision impairment.     

Infants’ sensitivity to familiar size: The effect of memory on spatial perception

Two experiments investigated infants’ sensitivity to familiar size as information for the distances of objects with which they had had only brief experience. Each experiment had two phases: a familiarization phase and a test phase. During the familiarization phase, the infant played with a pair of different-sized objects for 10 min. During the test phase, a pair of objects, identical to those seen in the familiarization phase but now equal in size, were presented to the infant at a fixed distance under monocular or binocular viewing conditions. In the test phase of Experiment 1, 7-month-old infants viewing the objects monocularly showed a significant preference to reach for the object that resembled the smaller object in the familiarization phase. Seven-month-old infants in the binocular viewing condition reached equally to the two test phase objects. These results indicate that, in the monocular condition, the 7-month-olds used knowledge about the objects’ sizes, acquired during the familiarization phase, to perceive distance from the test objects’ visual angles, and that they reached preferentially for the apparently nearer object. The lack of a reaching preference in the binocular condition rules out interpretations of the results not based on the objects’ perceived distances. The results, therefore, indicate that 7-month-old infants can use memory to mediate spatial perception. The implications of this finding for the debate between direct and indirect theories of visual perception are discussed. In the test phase of Experiment 2,5-month-old infants viewing the objects monocularly showed no reaching preference. These infants, therefore, showed no evidence of sensitivity to familiar size as distance information.     

Remembering more than meets the eye: a study of memory confusions about incomplete visual information

The purpose of this series of four experiments was to examine the possible role of spontaneous imagery in memory confusions about the way in which visual information had been experienced. After viewing pictures of familiar objects, complete or incomplete in visual form, participants were asked to remember the way in which the objects had been presented. Although, as predicted, memory for the objects themselves was quite good, participants falsely remembered seeing complete versions of pictures that were actually presented as incomplete. These false reports were observed across a variety of encoding and testing conditions. The results suggest that the false reports (referred to here as completion errors) are due to internal representations based on filling-in processes in response to the encoding of incomplete visual information. As such, the results also speak to alternative explanations for the completion errors and, more broadly, to theoretical perspectives that draw on filling-in processes when accounting for object identification and object memory.     

Distance estimation from cognitive maps

Four experiments investigated map clutter as a source of distortion in subjects' estimates of distance. In Experiments 1 (incidental learning) and 2 (intentional learning), subjects estimated distances between pairs of points on a memorized map. In both experiments, estimates increased as a linear function of the number of intervening points along the route. In Experiment 3, subjects estimated distances while viewing the map. The effect of clutter was reduced but not eliminated. In Experiment 4, the clutter effect was demonstrated using subjects' preexperimental knowledge of United States geography. Psychophysical power functions relating true to estimated distance provided a good fit to both memory and perception data. These results suggest an analogy between perceptual and memorial processes of distance estimation. A model proposed to account for the data assumes that subjects perceptually scan a route (or image of a route) from start to destination and use scan duration to determine path distance.     

Remembering more than meets the eye: A study of memory confusions about incomplete visual information

The purpose of this series of four experiments was to examine the possible role of spontaneous imagery in memory confusions about the way in which visual information had been experienced. After viewing pictures of familiar objects, complete or incomplete in visual form, participants were asked to remember the way in which the objects had been presented. Although, as predicted, memory for the objects themselves was quite good, participants falsely remembered seeing complete versions of pictures that were actually presented as incomplete. These false reports were observed across a variety of encoding and testing conditions. The results suggest that the false reports (referred to here as completion errors) are due to internal representations based on filling-in processes in response to the encoding of incomplete visual information. As such, the results also speak to alternative explanations for the completion errors and, more broadly, to theoretical perspectives that draw on filling-in processes when accounting for object identification and object memory.     

The moon illusion: I. How high is the sky?

The most common explanations of the moon illusion assume that the moon is seen at a specific distance in the sky, which is perceived as a definite surface. A decrease in the apparent distance to the sky with increasing elevation presumably leads to a corresponding decrease in apparent size. In Experiment 1 observers (N = 24) gave magnitude estimates of the distance to the night sky at different elevations. The results did not support the flattened-dome hypothesis. In Experiment 2 observers (N = 20) gave magnitude estimates of the distance to the sky at points around a 360 degrees circle just above the horizon. The results were consistent with those of Experiment 1, and in addition, estimates were highly correlated with the physical distances of buildings at the horizon. In a third, control experiment, observers (N = 20) gave magnitude estimates of the distances of buildings at the horizon. A power function fit the relation between estimated and physical distance (exponent = 1.17) as well as the relation between estimates of the sky points above the buildings (Experiment 2) and estimates of building distances (exponent = .46). Taken together, the results disconfirm all theories that attribute the moon illusion to a "sky illusion" of the sort exemplified by the flattened-dome hypothesis.     

Properties of spatial representations: Data from sighted and blind subjects

Five questions concerning the properties of spatial representations are explored. (1) How accurately does a spatial representation correspond to the true scene? (2) If inaccurate, how does it differ? (3) Are representations of a familiar scene more accurate than those of an unfamiliar one? (4) Do representations of a scene currently in view differ from those retained in memory? (5) Do the representations of the blind have properties comparable to those-of the sighted? Seven sighted and 7 highly mobile blind subjects, all familiar with a room, and 6 sighted subjects unfamiliar with it, were asked to estimate the absolute distances between 10 salient objects in the room. The 14 familiar subjects made their estimates twice: while they were in the room, and while they were remote from it. Regression analyses showed that the estimates of all subjects had strong metric properties, being linearly related to true distance, with a true zero point; and multidimensional scaling showed that all subjects produced distance estimates that could be scaled in two dimensions to closely match the actual locations of the objects. Familiarity had no effect. The effect of location of testing was the same for both the sighted and the blind: all subjects displayed better spatial knowledge when tested in the room; and all subjects underestimated true distance substantially when tested out of the room. The results showed no qualitative differences as a function of blindness, at least for these highly skilled blind travelers.     

The flexible use of inductive and geometric spatial categories

The present study examined the flexibility with which people can adopt different category schemes in the spatial domain. In a location memory task, participants viewed and estimated the locations of four kinds of objects that were spatially grouped by object identity. This identity-based arrangement was either congruent or incongruent with the perceptually based, geometric categories that have been reported in previous research. Four experiments examined the conditions under which these different category schemes are used to inform estimates of locations. The results showed that use of identity information depended on the number of objects to be remembered during a trial: When one or two objects were remembered at a time, only geometric categories affected estimates, but when four objects were to be remembered, both geometric categories and identity groupings affected estimates. As memory load increases, participants rely on additional sources to inform their estimates of location.     

Mental representation in visual/haptic crossmodal memory: evidence from interference effects

Two experiments used visual-, verbal-, and haptic-interference tasks during encoding (Experiment 1) and retrieval (Experiment 2) to examine mental representation of familiar and unfamiliar objects in visual/haptic crossmodal memory. Three competing theories are discussed, which variously suggest that these representations are: (a) visual; (b) dual-code—visual for unfamiliar objects but visual and verbal for familiar objects; or (c) amodal. The results suggest that representations of unfamiliar objects are primarily visual but that crossmodal memory for familiar objects may rely on a network of different representations. The pattern of verbal-interference effects suggests that verbal strategies facilitate encoding of unfamiliar objects regardless of modality, but only haptic recognition regardless of familiarity. The results raise further research questions about all three theoretical approaches.     

Mental representation in visual/haptic crossmodal memory: evidence from interference effects

Two experiments used visual-, verbal-, and haptic-interference tasks during encoding (Experiment 1) and retrieval (Experiment 2) to examine mental representation of familiar and unfamiliar objects in visual/haptic crossmodal memory. Three competing theories are discussed, which variously suggest that these representations are: (a) visual; (b) dual-code—visual for unfamiliar objects but visual and verbal for familiar objects; or (c) amodal. The results suggest that representations of unfamiliar objects are primarily visual but that crossmodal memory for familiar objects may rely on a network of different representations. The pattern of verbal-interference effects suggests that verbal strategies facilitate encoding of unfamiliar objects regardless of modality, but only haptic recognition regardless of familiarity. The results raise further research questions about all three theoretical approaches.     

Perceived size of familiar objects and the theory of off-sized perceptions

In three experiments, I examined the claim (Gogel, 1969; Gogel & Newton 1969)that familiar objects viewed under reduced stimulus conditions frequently appear to be off-sized (i.e., larger or smaller.than normal). In Experiments 1 and 2, I presented images ofdifferent familiar objects, one at a time, at distances of .1. and 2 m from the observers. The images were normal-, large-, or small-sized versions of familiar objects, and the observers judged the perceived size of each object rela.tive to its familiar normal size. In Experiment 3, I presented normal-, large-, and small-sized versions of thesame familiar object at physical distances of 1 and 2 m. The pattern of size results was similar across the three experiments. In general, normal-sized objects appeared normal to small-sized at the 1-mdistance and small-sized at the 2-mdistance; small-sized objects appeared small-sized at the 1-m distance and even smaller at the 2-m distance; and large-sized objects appeared normal- to large-sized at the 1-m distance and normal- to small-sized at the 2-m distance. The distance results of Experiment 3 indicated that familiar size was an effective determinant of reported distance. These results are consistent with Gogel’s theory of off-sized perceptions and, more generally, with the claim that familiar size is not an important determinant of perceived size.     

You’re looking for what? Comparing search for familiar,nameable objects to search for unfamiliar,novel objects

Searching for items in one’s environment often includes considerable reliance on semantic knowledge. The present study examines the importance of semantic information in visual and memory search, especially with respect to whether the items reside in long-term or working memory. In Experiment 1, participants engaged in hybrid visual memory search for items that were either highly familiar or novel. Importantly, the relatively large number of targets in this hybrid search task necessitated that targets be stored in some form of long-term memory. We found that search for familiar objects was more efficient than search for novel objects. In Experiment 2, we investigated search for familiar versus novel objects when the number of targets was low enough to be stored in working memory. We also manipulated how often participants in Experiment 2 were required to update their target (every trial vs. every block) in order to control for target templates that were stored in long-term memory as a result of repeated exposure over trials. We found no differences in search efficiency for familiar versus novel objects when templates were stored in working memory. Our results suggest that while semantic information may provide additional individuating features that are useful for object recognition in hybrid search, this information could be irrelevant or even distracting when searching for targets stored in working memory.     

Memory advantage for produced words and familiar native accents

Our memory is better for words that we have read aloud than for words that we have read silently or have listened to. The present study tested this memory advantage for words with native accent markers that participants were either highly familiar or less familiar. As in previous studies, produced words were subsequently remembered better than listened-to words. In contrast to previous studies that involved a comparison of global foreign accents with standard native accents, in the present study words with highly familiar accent markers were remembered better than words with less familiar accent markers (Experiment 1). The familiar accent advantage was also found when participants could not hear their own productions during the training phase (Experiment 2). When tested with a week delay, produced words were still remembered better than listened-to words, but the advantage for words with familiar accent markers was no longer found (Experiment 3).     

Subjects' expectations,individual variability,and the scanning of mental images

The near-perfect correlation between mental imagery scanning times (averaged across subjects) and interobject distances on imaged maps has been cited as evidence for Kosslyn's (1981) analog theory of mental imagery. Present results (1) indicate that individual subjects' scanning-time/distance correlations vary as a function of instructional set (and, hence, a priori expectations), and (2) reveal a large degree of individual variability in scanning-time/distance correlations.     

Neural correlates of object indeterminacy in art compositions

Indeterminate art invokes a perceptual dilemma in which apparently detailed and vivid images resist identification. We used event-related fMRI to study visual perception of representational, indeterminate and abstract paintings. We hypothesized increased activation along a gradient of posterior-to-anterior ventral visual areas with increased object resolution, and postulated that object resolution would be associated with visual imagery. Behaviorally, subjects were faster to recognize familiar objects in representational than in both indeterminate and abstract paintings. We found activation within a distributed cortical network that includes visual, parietal, limbic and prefrontal regions. Representational paintings, which depict scenes cluttered with familiar objects, evoked stronger activation than indeterminate and abstract paintings in higher-tier visual areas. Perception of scrambled paintings was associated with imagery-related activation in the precuneus and prefrontal cortex. Finally, representational paintings evoked stronger activation than indeterminate paintings in the temporoparietal junction. Our results suggest that perception of familiar content in art works is mediated by object recognition, memory recall and mental imagery, cognitive processes that evoke activation within a distributed cortical network.