Parsing silhouettes: the short-cut rule.

Many researchers have proposed that, for the purpose of recognition, human vision parses shapes into component parts. Precisely how is not yet known. The minima rule for silhouettes (Hoffman & Richards, 1984) defines boundary points at which to parse but does not tell how to use these points to cut silhouettes and, therefore, does not tell what the parts are. In this paper, we propose the short-cut rule, which states that, other things being equal, human vision prefers to use the shortest possible cuts to parse silhouettes. We motivate this rule, and the well-known Petter's rule for modal completion, by the principle of transversality. We present five psychophysical experiments that test the short-cut rule, show that it successfully predicts part cuts that connect boundary points given by the minima rule, and show that it can also create new boundary points.     

Test of Petter's rule for perceived surface stratification

Petter's rule applies to two-dimensional patterns formed by two overlapping surfaces that alternatively appear in front of one another. It states that the surface with the shorter contours in the region where the surfaces look superimposed has a greater probability of appearing in front of the other surface. An experiment is reported the results of which show that Petter's rule is valid for chromatically homogeneous and for uniformly dense dotted patterns, and invalid for different kinds of chromatically inhomogeneous patterns. Petter's rule has been found to be valid when the overlapping surfaces have contours with gaps. It is proposed that Petter's rule derives from the dynamics of filling-in of contour gaps.     

A theory of dynamic occluded and illusory object perception

Humans see whole objects from input fragmented in space and time, yet spatiotemporal object perception is poorly understood. The authors propose the theory of spatiotemporal relatability (STR), which describes the visual information and processes that allow visible fragments revealed at different times and places, due to motion and occlusion, to be assembled into unitary perceived objects. They present a formalization of STR that specifies spatial and temporal relations for object formation. Predictions from the theory regarding conditions that lead to unit formation were tested and confirmed in experiments with dynamic and static, occluded and illusory objects. Moreover, the results support the identity hypothesis of a common process for amodal and modal contour interpolation and provide new evidence regarding the relative efficiency of static and dynamic object formation. STR postulates a mental representation, the dynamic visual icon, that briefly maintains shapes and updates positions of occluded fragments to connect them with visible regions. The theory offers a unified account of interpolation processes for static, dynamic, occluded, and illusory objects.     

Spatiotemporal integration and contour interpolation revealed by a dot localization task with serial presentation paradigm

The visual system seems to integrate information that is presented over time in a spatially fragmented fashion, with the result that observers are able to report the whole shape of objects. This research considers relations in space and time that allow the integrated percepts of complete objects. Specifically, temporal characteristics for spatiotemporal integration of illusory contour and spatial characteristics of interpolated contour are examined. A serial presentation paradigm and a dot localization task were used in two experiments; observers localized a probe dot relative to a perceived contour of an illusory object. Each of four inducing figures was briefly presented in a serial order to observers and the total time of the series was manipulated. In Experiment 1 short time ranges varied up to 180 ms, whereas longer times were examined in Experiment 2. Overall, the results demonstrate that a short time allows spatiotemporal integration, and that the perceived location of contour consistently shifts with time range. These experiments suggest that the mechanism of spatiotemporal integration operates on spatial integration as a limiting case.     

Modal and amodal completion generate different shapes

Mechanisms of contour completion are critical for computing visual surface structure in the face of occlusion. Theories of visual completion posit that mechanisms of contour interpolation operate independently of whether the completion is modal or amodal--thereby generating identical shapes in the two cases. This identity hypothesis was tested in two experiments using a configuration of two overlapping objects and a modified Kanizsa configuration. Participants adjusted the shape of a comparison display in order to match the shape of perceived interpolated contours in a standard completion display. Results revealed large and systematic shape differences between modal and amodal contours in both configurations. Participants perceived amodal (i.e., partly occluded) contours to be systematically more angular--that is, closer to a corner--than corresponding modal (i.e., illusory) contours. The results falsify the identity hypothesis in its current form: Corresponding modal and amodal contours can have different shapes, and, therefore, mechanisms of contour interpolation cannot be independent of completion type.     

The open-object illusion: size perception is greatly influenced by object boundaries

This study presents a new powerful visual illusion, in which simple “open” objects—ones with missing boundaries—are perceived as bigger than the same size, fully “closed” objects. In a series of experiments that employed a continuous-response adjustment procedure, it was found that the lack of vertical boundaries inflated the perceived width of an object, whereas the lack of horizontal boundaries inflated its perceived length. The effect was highly robust and it was replicated across different stimulus types and experimental parameters, with almost all observers exhibiting a strong effect. In contrast to the overestimation of the size of an object due to missing boundaries, the inclusion of inner boundaries within an object caused observers to underestimate its size, suggesting that filled space sometimes shrinks, rather than inflates, the perceived size of an object. The open-object illusion bears practical implications for graphics and design as well as important theoretical implications. Specifically, it indicates that the perception of an object’s area is not veridical but rather critically depends on contour closure. It is suggested that the visual system extends the missing boundaries of open contour objects, which results in an overestimation of the object’s size.     

Automatic priming for translation- and scale-invariant representations of object shape

A series of visual search experiments explored whether early visual processes are sensitive to the overall shape of objects. Previous work (Wolfe & Bennett, 1997) has suggested that information concerning overall shape is not coded in early vision. However, in Experiment 1, we demonstrate that these previous findings are explicable in terms of non-target heterogeneity rather than an absence of shape information in early vision. In Experiments 2 and 3, we demonstrate that shape similarity, rather than individual contour similarity, can determine search efficiency. In Experiments 4 and 5, we show that manipulating the contrast polarity of contours and defining shape using texture significantly impeded search for an odd-one-out shape. The implications of these results for shape processing in early vision are discussed.     

Petter's effect in patterns formed by outlined surfaces

In patterns formed by two equally colored or by two transparent overlapping surfaces of different size that alternately appear in front of one another, the larger surface has a greater probability of appearing in front of the smaller surface. This effect is known as Petter's effect. The present study found that Petter's effect also occurred in patterns formed by colorless outlined surfaces. In these patterns Petter's effect was smaller than in chromatically homogeneous patterns. The results agree with the possibility that Petter's effect occurred in patterns formed by outlined surfaces because relative size was a cue to visually perceived distance.     

Strength of visual interpolation depends on the ratio of physically specified to total edge length.

We report four experiments in which the strength of edge interpolation in illusory figure displays was tested. In Experiment 1, we investigated the relative contributions of the lengths of luminance-specified edges and the gaps between them to perceived boundary clarity as measured by using a magnitude estimation procedure. The contributions of these variables were found to be best characterized by a ratio of the length of luminance-specified contour to the length of the entire edge (specified plus interpolated edge). Experiment 2 showed that this ratio predicts boundary clarity for a wide range of ratio values and display sizes. There was no evidence that illusory figure boundaries are clearer in displays with small gaps than they are in displays with larger gaps and equivalent ratios. In Experiment 3, using a more sensitive pairwise comparison paradigm, we again found no such effect. Implications for boundary interpolation in general, including perception of partially occluded objects, are discussed. The dependence of interpolation on the ratio of physically specified edges to total edge length has the desirable ecological consequence that unit formation will not change with variations in viewing distance.     

Strength of visual interpolation depends on the ratio of physically specified to total edge length

We report four experiments in which the strength ofedge-interpoiat-ion in illusory figure displays was tested. In Experiment 1, we investigated the relative contributions of the lengths of luminance-specified edges and the gaps between them to perceived boundary clarity as measured by using a magnitude estimation procedure. The contributionaoLthese variables were found to be best characterized by a ratio of the length of luminance-specified contour to the length of the entire edge (specified plus interpolated edge). Experiment 2 showed that this ratio predicts boundary clarity for a wide range of ratio values and display sizes.There was no evidence that illusory figure boundaries are clearer in displays with small gaps than they are in displays with larger gaps and equivalent ratios. In Experiment 3, using a more sensitive pairwise comparison paradigm, we again found no such effect. Implications for boundary interpolation in general, including perception of partially occluded objects, are discussed. The dependence of interpolation on the ratio of physically specified edges to total edgelength has thedesirable eeological consequence that unit formation will not change with variations in viewing distance.     

A Kinematic Analysis of Goal-directed Prehension Movements Executed under Binocular,Monocular, and Memory-guided Viewing Conditions

Vision is critical for the efficient execution of prehension movements, providing information about: The location of a target object with respect to the viewer; its spatial relationship to other objects; as well as intrinsic properties of the object such as its size and orientation. This paper reports three experiments which examined the role played by binocular vision in the execution of prehension movements. Specifically, transport and grasp kinematics were examined for prehension movements executed under binocular, monocular, and no vision (memory-guided and open-loop) viewing conditions. The results demonstrated an overall advantage for reaches executed under binocular vision; movement duration and the length of the deceleration phase were longer, and movement velocity reduced, when movements were executed with monocular vision. Furthermore, the results indicated that binocular vision is particularly important during “selective” reaching, that is reaching for target objects which are accompanied by flanker objects. These results are related to recent neuro psychological investigations suggesting that stereopsis may be critical for the visual control of prehension.     

Interpolation processes in object perception: reply to Anderson (2007)

P. J. Kellman, P. Garrigan, & T. F. Shipley presented a theory of 3-D interpolation in object perception. Along with results from many researchers, this work supports an emerging picture of how the visual system connects separate visible fragments to form objects. In his commentary, B. L. Anderson challenges parts of that view, especially the idea of a common underlying interpolation component in modal and amodal completion (the identity hypothesis). Here the authors analyze Anderson's evidence and argue that he neither provides any reason to abandon the identity hypothesis nor offers a viable alternative theory. The authors offer demonstrations and analyses indicating that interpolated contours can appear modally despite absence of the luminance relations, occlusion geometry, and surface attachment that Anderson claims to be necessary. The authors elaborate crossing interpolations as key cases in which modal and amodal appearance must be consequences of interpolation. Finally, the authors dispute Anderson's assertion that vision researchers are misguided in using objective performance methods, and they argue that his challenges to relatability fail because contour and surface processes, as well as local and global influences, have been distinguished experimentally.     

Memory for curvature of objects: Haptic touch vs. vision

The present study examined the role of vision and haptics in memory for stimulus objects that vary along the dimension of curvature. Experiment 1 measured haptic‐haptic (T‐T) and haptic‐visual (T‐V) discrimination of curvature in a short‐term memory paradigm, using 30‐second retention intervals containing five different interpolated tasks. Results showed poorest performance when the interpolated tasks required spatial processing or movement, thereby suggesting that haptic information about shape is encoded in a spatial‐motor representation. Experiment 2 compared visual‐visual (V‐V) and visual‐haptic (V‐T) short‐term memory, again using 30‐second delay intervals. The results of the ANOVA failed to show a significant effect of intervening activity. Intra‐modal visual performance and cross‐modal performance were similar. Comparing the four modality conditions (inter‐modal V‐T, T‐V; intra‐modal V‐V, T‐T, by combining the data of Experiments 1 and 2), in a global analysis, showed a reliable interaction between intervening activity and experiment (modality). Although there appears to be a general tendency for spatial and movement activities to exert the most deleterious effects overall, the patterns are not identical when the initial stimulus is encoded haptically (Experiment 1) and visually (Experiment 2).     

Surface formation and depth in monocular scene perception

The visual perception of monocular stimuli perceived as 3-D objects has received considerable attention from researchers in human and machine vision. However, most previous research has focused on how individual 3-D objects are perceived. Here this is extended to a study of how the structure of 3-D scenes containing multiple, possibly disconnected objects and features is perceived. Da Vinci stereopsis, stereo capture, and other surface formation and interpolation phenomena in stereopsis and structure-from-motion suggest that small features having ambiguous depth may be assigned depth by interpolation with features having unambiguous depth. I investigated whether vision may use similar mechanisms to assign relative depth to multiple objects and features in sparse monocular images, such as line drawings, especially when other depth cues are absent. I propose that vision tends to organize disconnected objects and features into common surfaces to construct 3-D-scene interpretations. Interpolations that are too weak to generate a visible surface percept may still be strong enough to assign relative depth to objects within a scene. When there exists more than one possible surface interpolation in a scene, the visual system's preference for one interpolation over another seems to be influenced by a number of factors, including: (i) proximity, (ii) smoothness, (iii) a preference for roughly frontoparallel surfaces and 'ground' surfaces, (iv) attention and fixation, and (v) higher-level factors. I present a variety of demonstrations and an experiment to support this surface-formation hypothesis.     

Haptic experiences influence visually acquired memories: Reference frames during multimodal spatial learning

In two experiments, we investigated whether reference frames acquired through touch could influence memories for locations learned through vision. Participants learned two objects through touch, and haptic egocentric (Experiment 1) and environmental (Experiment 2) cues encouraged selection of a specific reference frame. Participants later learned eight new objects through vision. Haptic cues were manipulated, whereas visual learning was held constant in order to observe any potential influence of the haptically experienced reference frame on memories for visually learned locations. When the haptically experienced reference frame was defined primarily by egocentric cues, cue manipulation had no effect on memories for objects learned through vision. Instead, visually learned locations were remembered using a reference frame selected from the visual study perspective. When the haptically experienced reference frame was defined by both egocentric and environmental cues, visually learned objects were remembered in the context of the haptically experienced reference frame. These findings support the common reference frame hypothesis, which proposes that locations learned through different sensory modalities are represented within a common reference frame.     

Touching for knowing in infancy: The development of manual abilities in very young infants

This aim of this paper was twofold: (1) to display the various competencies of the infant's hands for processing information about the shape of objects; and (2) to show that the infant's haptic mode shares some common mechanisms with the visual mode. Several experiments on infants from birth and up to five months of age using a habituation/dishabituation procedure, intermodal transfer task between touch and vision, and various cognitive tasks revealed that infants may perceive and understand the physical world through their hands without visual control. From birth, infants can habituate to shape and detect discrepancies between shapes. But information exchanges between vision and touch are partial in cross-modal transfer tasks. Plausibly, modal specificities such as discrepancies in information gathering between the two modalities and the different functions of the hands (perceptual and instrumental) limit the links between the visual and haptic modes. In contrast, when infants abstract information from an event not totally felt or seen, amodal mechanisms underlie haptic and visual knowledge in early infancy. Despite various discrepancies between the sensory modes, conceiving the world is possible with hands as with eyes.     

Visually guided grasping of common objects: Effects of priming

Priming effects were tested on the planning of the grasping of common objects under full vision during action performance. Healthy participants took part in four experiments which manipulated the nature of the prime (objects, circular block, rectangular bar) and priming context (blocked vs. mixed). Each experiment relied on four priming conditions: (1) congruent orientation, (2) incongruent orientation, (3) neutral prime, and (4) no prime. Priming was observed to have a facilitating effect on visually guided grasping when the object to be grasped was primed by a congruently oriented identical object. This effect was rather independent of the priming context (experimental set-up). Our data suggest an object's functional identity may contribute to the priming effect, as well as its intrinsic (e.g., shape, size) and extrinsic (orientation) visual characteristics. We showed that the planning of visually guided grasping is influenced by prior visual experience, and thus that grasping is not based exclusively on real-time processing of visual information.     

Does rule recursion make melodies easier to reproduce? If not, what does?

Two experiments examined the effects of variations in melodic rule structure and rhythm upon the ability of musically sophisticated listeners to reproduce auditory patterns. These experiments were designed to evaluate different theoretical perspectives on auditory pattern perception and the role of rule structure in perceiving and remembering. Predictions of a coding model, which emphasizes the impact of rule recursion, were contrasted with those of an accent model, which emphasizes the relative timing of melodic and temporal accents. Effects of recursive (hierarchical) and nonrecursive (linear) rule arrangements were studied in contexts where pattern contour differences were controlled for. Rhythm was also varied. Measured pauses were inserted between certain tones to make a rhythm compatible or incompatible with melodic rule phrases. Experiment 1 showed that pattern simplicity was determined not by rule recursive codes, but by the number and timing of contour changes and melodic rule breaks. Experiment 2 examined additional effects of rhythm on listeners' response to rule recursion and melodic phrasing in melodies of equivalent contour. Although modest effects of rule recursion appeared, these effects were again outweighed by large performance differences due to the relative timing of changes in contour and melodic rule structure. Implications of the accent model for dynamic attending are discussed in the context of a new proposal involving temporal phasing of accents.     

The role of contour polarity,objectness, and regularities in haptic and visual perception

Regularities like symmetry (mirror reflection) and repetition (translation) play an important role in both visual and haptic (active touch) shape perception. Altering figure-ground factors to change what is perceived as an object influences regularity detection. For vision, symmetry is usually easier to detect within one object, whereas repetition is easier to detect across two objects. For haptics, we have not found this interaction between regularity type and objectness (Cecchetto & Lawson, Journal of Experimental Psychology: Human Perception and Performance, 43, 103–125, 2017; Lawson, Ajvani, & Cecchetto, Experimental Psychology, 63, 197–214, 2016). However, our studies used repetition stimuli with mismatched concavities, convexities, and luminance, and so had mismatched contour polarities. Such stimuli may be processed differently to stimuli with matching contour polarities. We investigated this possibility. For haptics, speeded symmetry and repetition detection for novel, planar shapes was similar. Performance deteriorated strikingly if contour polarity mismatched (keeping objectness constant), whilst there was a modest disadvantage for between-2objects:facing-sides compared to within-1object:outer-sides comparisons (keeping contour polarity constant). For the same task for vision, symmetry detection was similar to haptics (strong costs for mismatched contour polarity, weaker costs for between-2objects:facing-sides comparisons), but repetition detection was very different (weak costs for mismatched contour polarity, strong benefits for between-2objects:facing-sides comparisons). Thus, objectness was less influential than contour polarity for both haptic and visual symmetry detection, and for haptic repetition detection. However, for visual repetition detection, objectness effects reversed direction (within-1object:outer-sides comparisons were harder) and were stronger than contour polarity effects. This pattern of results suggests that regularity detection reflects information extraction as well as regularity distributions in the physical world.