Coding theory of visual pattern completion

It is possible to construct a line drawing that represents one object partly hidden behind another, and most subjects complete the interrupted figure and see the hidden object as whole. This article is addressed to two problems: (a) What are the necessary and sufficient conditions for such figural completion to occur, and (b) exactly what will be seen behind the occluding figure---that is, what completion will be made? Leeuwenberg's coding model for line drawings was used to analyze a number of such figures, along with the hypothesis that figural completion occurs whenever it results in a simplification of final code of the whole figure. Data from previous experiments along with results from two new experimental studies were collected and shown to agree with this hypothesis. Of various possible figural completions or "mosaic" interpretations, subjects chose the ones resulting in the simplest overall code. However, the above conclusions are correct only if "simple" is precisely defined as the smallest information load in a completely reduced code. Other possible theories of figural completion, both structuralist and Gestalt, may invoke familiarity, particular "cues," like T-shaped intersections, simplicity of the hidden figure, symmetry, and good continuation. All such possibilities were considered in the experiments and shown to fail, wrongly predicting at least one figure. The coding-theory analysis, on the other hand, made correct predictions for all of the 25 figures used.     

The minimum principle and visual pattern completion

Summary The minimum principle states that a perceiver will see the simplest possible interpretation of a pattern. Some theorists of human perception take this principle as a core-explanatory concept. Others hold the view that a perceptual minimum principle is untenable. In two recent extensive surveys of the relevant literature a more differentiated position is taken: the minimum principle is not renounced in a definite way. In the research reported here, an intuitively appealing specification of a minimum principle is tested. An experiment on visual pattern completion was performed in which patterns were presented to subjects who traced the contours of the shapes they saw. It was predicted that there would be a preference for interpretations that describe a pattern as a set of separate shapes with minimal information load as computed by Leeuwenberg's coding language. However, only half of the responses given by the subjects were predicted by this specification of a minimum principle. It was further demonstrated that locally complex interpretations of junctions of contour elements are easily made, but not in order to attain globally minimal interpretations.     

Representation versus process in simplicity of serial pattern completion

This study deals with the question whether preferred extrapolations of serial patterns are determined by the extrapolation process or the representation of serial patterns. Three experiments are reported. The first deals with series of letters from the alphabet. Each series gave rise to extrapolations with varying frequencies, and we investigated how well these frequencies are predicted by the information loads, stemming from three models. The model of Klahr and Wallace (1970) is mainly concerned with the process of extrapolation. The model of Simon and Kotovsky (1963) describes both the process and the representation of extrapolated series. A third model is introduced here that exclusively deals with the representation of series. The outcome indirectly indicates that the preferred extrapolation is determined by the simplest representation of a series and not by the simplest process towards this representation. To strengthen the last conclusion two experiments are added dealing with bar graph stimuli. They are designed to experimentally disentangle representation and process complexity. In the second experiment the task was to judge the complexity of each series after having extrapolated the series. In the third experiment, subjects had to judge complexity of extrapolated series without the task to extrapolate the series. The predictions from the three models make plausible that the complexity judgments of second experiment reflect the process of extrapolation and the complexity judgments of the third experiment still reflect the representation of series. The latter results again support the assumption that the preferred extrapolation is determined by the simplest representation of a series.     

Local and global orientation in visual search

Six experiments investigated the role of global (shape) and local (contour) orientation in visual search for an orientation target. Experiment 1 demonstrated thatsearch for a conjunction of local contours with a distinct global orientation was less efficient than search for a target featurally distinct in terms of both global and local contour orientation. However, Experiments 2 and 4 demonstrated that the presence of a unique line contour was neither sufficient nor necessary to allow efficient search. Experiment 5 found thatsearch for a local orientation difference was strongly impeded by irrelevant variation in global orientation, arguing for a preeminent role for global orientation. Finally, Experiment 6 demonstrated that the orientation search asymmetry holds for the global orientation of stimuli. Taken together, the results are consistent with visual search processes guided predominately by a representation of global orientation.     

Local and global factors of similarity in visual search

Effects of the similarity between target and distractors in a visual search task were investigated in several experiments. Both familiar (numerals and letters) and unfamiliar (connected figures in a 5 × 5 matrix) stimuli were used. The observer had to report on the presence or absence of a target among a variable number of homogeneous distractors as fast and as accurately as possible. It was found that physical difference had the same clear effect on processing time far familiar and for unfamiliar stimuli: processing time decreased monotonically with increasing physical difference. Distractors unrelated to the target and those related to the target by a simple transformation (180° rotation, horizontal or vertical reflection) were also compared, while the physical difference was kept constant. For familiar stimuli, transformational relatedness increased processing time in comparison with that fort unrelated stimulus pairs. It was further shown in a scaling experiment that this effect could be accounted for by the amount of perceived similarity of the target-distractor pairs. For unfamiliar stimuli, transformational relatedness did have a smaller and less pronounced effect. Various comparable unrelated distractors resulted in a full range of processing times. Results from a similarity scaling experiment correlated well with the outcome of the experiments with unfamiliar stimuli. These results are interpreted in terms of an underlying continuum of perceived similarity as the basis of the speed of visual search, rather than a dichotomy of parallel versus serial processing.     

Investigating metrical and structural aspects of visual completion: Priming versus searching

Earlier research on visual occlusion showed some flexibility in the formation of visual completions, as long as the structural aspects (e.g., symmetry) of the visible part of the partly occluded shape were preserved in the completion (de Wit & van Lier, ). In this study, we examined whether changing the overall size of the occluded shape would preserve the overall structure. In Experiment 1, using the primed‐matching paradigm, we found evidence for relative size invariance in the completion process. To investigate whether changes in the structural aspects of shape are generally more salient than those of size, we employed the same stimuli in visual search and change detection paradigms. Experiment 2 demonstrated effects of completion in both paradigms. Experiment 3 showed that the metrical aspects of the shapes used in Experiment 1 are nevertheless detected faster than the structural aspects under search conditions. Because the variation in structural aspects is not more salient than in metrical aspects, we conclude that for these shapes, visual completion is indeed size‐invariant. The relations between performances in the three paradigms are discussed.     

Simple drawing and pattern completion techniques for studying visualization and long-term visual knowledge

Simple and efficient drawing and completion tasks for studying visual memory are developed. In Experiment I subjects reproduced a series of matrix patterns by filling empty matrices. The serial position function was fiat, except that accuracy was much higher for final patterns. In Experiment 2 this recency effect was removed by an interpolated pattern classification task. Experiments 3 and 4 examined the effect of counting backward during intervals of from 3 to 15 sec on the recall of single patterns. Drawings were much less accurate after filled intervals but the duration of the interval had no effect. Experiment 5 tested retention of series of patterns using a completion task. On immediate test the serial position function was the same as in Experiments 1 and 2. On a final test accuracy was unchanged except for final items, which then showed a small negative recency effect. It is argued that performance is so similar in the drawing, completion, and previously reported recognition tasks because in all it is based upon the use of general-purpose knowledge accessible to voluntary processing. Visualization in these tasks is analogous to but different from verbal STM. One main difference is that there is no sign of temporary storage of visualized information after attention has turned to other things.     

Local and global visual mechanisms underlying individual differences in the rod-and-frame illusion

The role of local and global visual mechanisms in individual differences in the rod-and-frame (RF) effect was investigated. Field-dependent and field-independent observers, selected on the basis of Witkin and Asch’s (1948) classical procedure, were submitted to the small RF test (Coren & Hoy, 1986). Four frame tilts and two gap sizes were used. As expected, direct effects (i.e., rod settings in the direction of frame tilt) were observed at small degrees of frame tilt, while indirect effects (i.e., rod settings in the direction opposite that of frame tilt) were observed at larger frame tilts. Fielddependent observers showed larger direct effects in the case of the small gap. Indirect effects were comparable in both field-dependent and field-independent subjects, regardless of gap size. Following the model proposed by Wenderoth and Johnstone (1987), these findings indicate that low-level visual mechanisms, responsible for local orientation interactions, have a different gain in fielddependent and field-independent individuals. In contrast, global visual mechanisms, presumably acting     

Global visual completion of quasi-regular shapes

The topic of amodal completion has often been investigated by using partly occluded shapes that are regular. In research that has typically been done with displays such as these regular shapes, it has been shown that global aspects of a shape can determine completion. To see how robust these global influences in the completion process are, we investigated quasi-regular shapes, ie shapes with a certain overall regularity but not based on metrical identities. First, in experiment 1 participants had to complete quasi-regular shapes in a drawing task. Then, in experiment 2 the primed-matching paradigm was used. Results from both experiments provided evidence for global completions. In experiment 3 we found that multiple global completions can be primed, which, as a control experiment showed, cannot be explained by some inability of the visual system to see the difference between the different completions. These data support the notion that global influences on visual occlusion are apparent even when the partly occluded stimulus is outside the domain of regular shapes. Implications for a global approach are provided.     

Local versus global processing of harmonic cadences in the solution of musical puzzles

The structure of Western musical pieces is delineated by several kinds of cadence. Half cadences in the main key indicate temporary endings; authentic cadences in the main key indicate definitive endings. Authentic cadences in the dominant key are of cognitive interest, since they mark a definitive ending at a local level but a temporary ending at a global level. This study investigated the local versus global processing of these cadences. Participants were presented with sections of 16-bar minuets displayed on a computer screen in the form of a musical jigsaw puzzle. The sections consisted of either the first or the second half of the minuet (8 bars each). The first section ended with either a half cadence in the main key (all experiments), an authentic cadence in the dominant key (all experiments), or an authentic cadence in the main key (Exp. 4). The second section always ended in an authentic cadence in the main key. Participants were asked either to join the two sections of each minuet in the most coherent order (Exps. 1, 2, 4) or to rate the perceived completion of each section (Exps. 3, 4). Numerous inversion errors were observed when the first section of the minuets ended with an authentic cadence in the dominant key. Completion judgments indicated that these cadences were perceived as marking a definitive ending. Both facts suggest that local processing of harmonic cadences prevails over global processing. This finding concurs with recent studies showing that listeners had great difficulties in perceiving the higher-order organization of musical form. Received: 30 September 1996 / Accepted: 20 August 1997     

Implicit memory for phonological processes in visual stem completion

Four experiments were conducted investigating the role of phonology in repetition priming. Experiment 1 used a cross-modal priming paradigm in which participants made semantic judgments about spoken words and then performed a visual stem completion task. In Experiments 2–4, both the primes and the test stems were presented visually. The results of the first three experiments revealed that priming transfers across interpretations of a homophone. That is, seeing or hearingweek primes bothweek andweak. The results of Experiment 4 showed that homophone priming cannot be attributed to the orthographic similarity of homophonic words. Together, these results indicate that repetition priming on a visual word completion task includes a phonological component.     

Perceptual completion and object-based representations in short-term visual memory

Object-based representations in visual short-term memory (VSTM) were examined using a change detection memory task. A display comprising two rows of four differently colored elements was followed by a probe display in which only one of the rows reappeared. On same trials, the probed row was identical to the corresponding row in the memory display. On different trials, two of the elements in the probed row had their colors exchanged. In each memory display, a task-irrelevant visual element appeared between the two rows, with the potential to function as an occluder. Performance was enhanced when perceptual completion meant that four, rather than eight, objects were perceived in the memory display and when the probe display revealed that the occluded elements continued behind the occluder. It appears that several forms of representation can co-occur to support VSTM, one of which is object based.     

Luminance edges are not necessary for visual completion

Luminance edges seem to have an important role in visual feature binding and, more specifically, in visual completion because luminance differences are important for the perception of depth. We investigated this claim in two experiments in which the primed-matching paradigm was used. In Experiment 1, we investigated conditions under which either a partly occluded shape or an occluder was isoluminant with respect to the background. In Experiment 2, the partly occluded shape and the occluder were isoluminant with respect to each other. Evidence was found for visual completion in all cases, and we therefore conclude that luminance edges are not essential for visual completion.     

Local autonomy in visual space

Abstract.— The adjacency principle is considered in the context of the two factor theory of perception which divides the sources of perceptual information into absolute and relative cues. The adjacency principle states that the effectiveness of relative cues between objects varies inversely with the perceived separation of the objects either in a frontoparallel plane or in depth. The evidence regarding this principle is discussed for paradigms in which a test object is displaced spatially with respect to either one induction object or two opposing induction objects. The mqjor cues examined for evidence regarding adjacency effects consists of binocular disparity, achromatic color induction. and relative motion.     

Modality-specificity effects in priming of visual and auditory word-fragment completion

In this study, the researchers examined modality-specificity effects in priming of visual and auditory word-fragment completion by the presentation of visual or auditory primes. In 2 experiments, within-modality priming and cross-modality priming were observed, with greater priming observed in the within-modality conditions. The prime was presented in a word list in Experiment 1 and either presented or inferred in priming sentences in Experiment 2. Inferring a target that was not actually presented in the sentences resulted in priming of fragment completion but not in modality specificity. These results, coupled with comparisons to explicit cued fragment completion, support the interpretation that priming of word-fragment completion is owing to both a perceptual and a nonperceptual component. This latter component may be different than the conceptual processes used for explicit memory, which did show modality specificity for inferred targets.     

Local rather than global processing of visual arrays in numerosity discrimination by pigeons (Columba livia)

A series of experiments investigated which stimulus properties pigeons use when they discriminate pairs of visual arrays that differ in numerosity. Transfer tests with novel stimuli confirmed that the birds’ choices were based on relative differences in numerosity. However, pigeons differed from other species in the non-numerical cues that affected their choices. In human and non-human primates, numerical discrimination is often influenced by continuous variables such as surface area or overall stimulus brightness. Pigeons showed little evidence of using those cues, even when summed area and brightness had been correlated with numerosity differences and reward outcome. But when array-element sizes were asymmetrically distributed across numerosities, the birds readily utilized information about item sizes as an additional discriminative cue. These novel results are discussed in relation to pigeons’ tendency to focus on local, rather than global dimensions when they process other non-numerical complex visual stimuli. The findings suggest there may be inter-specific differences in the type of perceptual information that provides the input stage for mechanisms underlying numerical processing. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Attending to the big picture: mood and global versus local processing of visual information

Two experiments employed image-based tasks to test the hypothesis that happier moods promote a greater focus on the forest and sadder moods a greater focus on the trees. The hypothesis was based on the idea that in task situations, affective cues may be experienced as task-relevant information, which then influences global versus local attention. Using a serial-reproduction paradigm, Experiment 1 showed that individuals in sad moods were less likely than those in happier moods to use an accessible global concept to guide attempts to reproduce a drawing from memory. Experiment 2 investigated the same hypothesis by assessing the use of global and local attributes to classify geometric figures. As predicted, individuals in sad moods were less likely than those in happier moods to classify figures on the basis of global features.     

Size scaling in visual pattern recognition

Human visual recognition on the basis of shape but regardless of size was investigated by reaction time methods. For successive matching of random figures, reaction time increased linearly with the linear size ratio of stimulus pairs. For single-character classification, reaction time increased with divergence between cued size format and stimulus format such that for character nonrepetitions, the increment in latency was approximately proportional to the logarithm of the linear size ratio of the two formats. However, when reactions to character repetitions were faster than those to nonrepetitions, the repetition reaction time function was similar to that for successive matching of random figures. The results suggested two processes of size scaling: mental-image transformation and perceptual-scale transformation. Image transformation accounted for matching performance based on visual short-term memory, whereas scale transformation accounted for size invariance in recognition based on comparison against visual representations in long-term memory.     

The effect of a modal completion on visual matching

In a series of five experiments, we investigated how amodal completion affects pattern recognition, and tested possible models of processes underlying completion of simple shapes. Inferences about processing models were based mainly upon the comparison of ‘same’ latencies in a simultaneous matching task. The major result of experiments 1–4 regards two conditions where a complete target had to be matched with a given stimulus region, belonging to a composite comparison pattern. Matching is faster when this stimulus region is amodally completed than when it looks like an incomplete shape. In experiment 5 we compared complete vs incomplete targets, that were either phenomenally or topographically identical to a given region of the comparison pattern. The failure to show any effect of target completeness suggests that phenomenal identity may be as effective as topographical identity.