Phonemic confusability,precategorical acoustic storage,and the suffix effect

Ss attempted ordered recall of acoustically presented strings of seven consonant-vowel syllables. In a control condition, each string was followed by a tone in presentation, while in the experimental (suffix) conditions, a verbal syllable followed the last to-be-remembered item. The independent variable was the phonemic similarity between the verbal suffix and the memory stimuli Although the verbal syllables produced a large suffix effect as compared with the control condition, and although more errors were made overall when similarity was high, the degree to which the verbal suffix items reduced the recency advantage at the end of the series was independent of their phonemic similarity to the stimuli. This independence was taken as support for a distinction between acoustic and articulatory coding.     

Perceptual organization and attention

It is widely assumed that the grouping of the visual field first described by the Gestalt psychologists and the related phenomenon of texture segregation occur very early in the processing of visual information and involve preattentive processes. All the recent evidence supporting this assumption comes from visual search experiments in which the subject is actively looking for a target and attending to the stimulus. The question at issue is whether these kinds of patterns are perceived under conditions of inattention, i.e., when observers are not searching for them. We performed six experiments to determine whether texture segregation and grouping by similarity or proximity are perceived under conditions of inattention. On the first two trials subjects were asked to report the longer arm of a briefly presented cross which was surrounded by a pattern of ungrouped small elements. On the third trial and subsequent control trials these elements were configured into grouping patterns and subjects queried about them immediately following their line length reports. The results establish that neither texture segregation nor grouping by similarity of lightness or proximity are perceived under conditions of inattention. They support the conclusion that there is an earlier stage of processing than that referred to as preattentive.     

Perceptual organization and White's illusion

The apparent lightness of a surface can be strongly modulated by the spatial context in which it is embedded. Early theories of such context dependence emphasized the role of low-level mechanisms that sense border contrast, whereas a number of recent authors have emphasized the role of perceptual organization in determining perceived lightness. One of the simplest and most theoretically challenging lightness illusions was described by White. This illusion has been explained with a variety of different models, ranging from low-level filter outputs to computations underlying the extraction of mid-level representations of surfaces. Here, I present a new method for determining the organizational forces that shape this illusion. I show that the spatial context of White's pattern not only transforms the apparent lightness of homogeneous target patches. but can also induce dramatic inversions of figure-ground relationships of textured target regions. These phenomena provide new evidence for the role of scission in causing the lightness illusion experienced in White's effect.     

Perceptual organization and schizotypy.

The preattentive visual information processing of hypothetically psychosis-prone college subjects was evaluated using three different paradigms, target detection (n = 57), visual suffix effect (n = 57), and configural superiority effect (n = 68). It was hypothesized that anhedonic subjects would show the same perceptual organization deficits reported in process schizophrenics and that perceptual aberration-magical ideation subjects and depressed subjects would perform similarly to control subjects. In each study, anhedonics performed similarly to each comparison group, even though there was adequate power to detect performance differences if they existed. A framework for understanding the visual information-processing deficits of schizophrenics and high-risk subjects is proposed.     

Perceptual organization of two-dimensional patterns

The perceptual organization of image patterns is considered from 2 standpoints. First, a theoretical framework is presented from which computational models of perceptual organization can be constructed and tested. Second, a specific computational model for perceptual organization of line images is described. In this model, input images are first processed by a dense array of neurons that have properties consistent with recent analyses of single-neuron responses in primary visual cortex. Then, complex image structure is discovered by interleaved pattern-matching and grouping processes constrained by a generalized uniqueness principle. A series of 3-pattern grouping experiments was performed to test a restricted version of the model and to estimate critical parameters. Using the estimated parameters, an extended version of the model was tested by generating predictions for a series of "textbook" perceptual organization demonstrations.     

Perceptual organization in task performance

Models of job cognition have neglected the perceptual process by which units of task behavior are organized prior to making task judgments. Perceptual organization was examined in this study using an unobtrusive observational technique adapted from the psycholinguistic literature. In each of two experiments, the structure of a task was manipulated to vary the relationship between task behavior and feedback. These manipulations were found to be reflected in the measure of perceptual organization. In Experiment 2, perceptual organization was found also to correlate with higher order judgments about the task. The implications of these results for expanding models of job cognition to include perceptual processes are discussed.     

Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): I. Pure tones

A new combination of operant conditioning and psychophysical scaling procedures was used to study auditory perception in a small bird. In a same-different discrimination task, budgerigars learned to discriminate among pure tones that varied along one or more acoustic dimensions. Response latencies were used to generate a matrix of interstimulus similarities. Multidimensional scaling procedures were used to arrange these acoustic stimuli in a multidimensional space that supposedly reflects the bird's perceptual organization. For tones that varied in intensity, duration, and frequency simultaneously, budgerigars were much more sensitive to frequency changes. From a set of tones that varied only in intensity, it was possible to calculate the growth of loudness with intensity for the budgerigar. For tones that varied only in frequency, budgerigars showed evidence of an "acoustic fovea" for frequency change in the spectral region of 2-4 kHz. Budgerigars and humans also differed in their perceptual grouping of tone sequences that rise, fall, or remain constant in pitch. Surprisingly, budgerigars were much less responsive to pitch contour than were humans.     

Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): III. Contact calls

We trained budgerigars by operant conditioning to discriminate among a set of contact calls in a same-different task and analyzed response latencies from this task by using multidimensional-scaling (MDS) and cluster-analysis procedures. Humans listened to the same calls and indicated the similarity between pairs of calls by a direct rating procedure. An MDS program (sindscal) was used to arrange these complex acoustic stimuli in multidimensional space reflecting perceptual organization. Multiple regression techniques were used to identify the acoustic characteristics of contact calls that were correlated with the perceptual dimensions obtained from MDS. A number of spectral characteristics (e.g., peak frequency, rate of frequency modulation, and concentration of spectral energy) emerged as important for both budgerigars and humans, but the relative salience of these cues differed for the two species. Additional tests with two groups of budgerigars--cagemates and noncagemates--showed that experience with calls can change the salience of various acoustic characteristics used for perceptual organization and individual recognition.     

Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): II. Vocal signals

Operant conditioning and multidimensional scaling procedures were used to study auditory perception of complex sounds in the budgerigar. In a same-different discrimination task, budgerigars learned to discriminate among natural vocal signals. Multidimensional scaling procedures were used to arrange these complex acoustic stimuli in a two-dimensional space reflecting perceptual organization. Results show that budgerigars group vocal stimuli according to functional and acoustical categories. Studies with only contact calls show that birds also make within-category discriminations. The acoustic cues in contact calls most salient to budgerigars appear to be quite complex. There is a suggestion that the sex of the signaler may also be encoded in these calls. The results from budgerigars were compared with the results from humans tested on some of the same sets of complex sounds.     

Perceptual organization in multistable apparent motion

Is motion perception based on a local piecemeal analysis of the image or do 'global' effects also play an important role? Use was made of bistable apparent-motion displays in trying to answer this question. Two spots were flashed simultaneously on diagonally opposite corners of a 1 deg wide square and then switched off and replaced by two spots appearing on the other two corners. One can either see vertical or horizontal oscillation and the display is bistable just as a Necker cube is. If several such bistable figures are randomly scattered on the screen and presented simultaneously, then one usually sees the same motion axis in all of them, suggesting the presence of field-like effects for resolving ambiguity in apparent motion. While viewing a single figure observers experience hysteresis: they tend to adhere to one motion axis or the other and can switch the axis only by looking away and looking back after 10-30 s have elapsed. The figure can be switched off and made to reappear at some other random location on the screen and it is then always found to retain its motion axis. Several such demonstrations are presented to show that spatial induction effects in metastable motion displays may provide a particularly valuable probe for studying 'laws' of perceptual organization.     

Perceptual organization influences visual working memory

Previous studies have demonstrated that top-down factors can bias the storage of information in visual working memory. However, relatively little is known about the role that bottom-up stimulus characteristics play in visual working memory storage. In the present study, subjects performed a change detection task in which the to-be-remembered objects were organized in accordance with Gestalt grouping principles. When an attention-capturing cue was presented at the location of one object, other objects that were perceptually grouped with the cued object were more likely to be stored in working memory than were objects that were not grouped with the cued object. Thus, objects that are grouped together tend to be stored together, indicating that bottom-up perceptual organization influences the storage of information in visual working memory.     

Precategorical acoustic storage and postcategorical lexical storage

A variety of experimental findings have indicated that a system of precategorical acoustic storage is responsible for the recency effect obtained in the immediate serial recall of sequences of digits, consonants, or syllables. This study investigated whether such findings could be generalized to the recall of sequences of words. Experiment 1 showed that phonemic similarity among a sequence of words failed to reduce the modality effect or the recency effect. Experiment 2 demonstrated that this finding was not attributable to a failure to control the phonemic properties of the stimulus material. Experiment 3 showed that the stimulus suffix effect obtained with sequences of words was not affected by the acoustic similarity between the list items and the stimulus suffix. Finally, Experiment 4 demonstrated that phonemic similarity among a sequence of words failed to reduce the stimulus suffix effect. These results were explained by extending the original model of short-term memory to incorporate a system of postcategorical lexical storage.     

Perceptual organization and apparent brightness in subjective contour figures

According to a number of theories subjective contours arise from brightness contrast and/or assimilation. The apparent brightness gradients generated by these effects are assumed to give rise to the perception of contours delineating the gradients. A study is reported in which naive observers were shown a subjective contour display and asked to report what they saw. They were then asked to judge whether the center or the surround of the display appeared brighter. Subjects whose reports indicated that they had seen the subjective contour figure showed an overwhelming preference for the center of the display being brighter than the surround. However, subjects who did not see the subjective contour figure did not differ significantly in their selection of the center over the surround. This finding presents difficulties for any theory which derives subjective contours from the apparent brightness difference.     

Perceptual organization and artificial attention for visual landmarks detection

In biological vision systems, attention mechanisms are responsible for selecting the relevant information from the sensed field of view, so that the complete scene can be analyzed using a sequence of rapid eye saccades. In recent years, efforts have been made to imitate such attention behavior in artificial vision systems, because it allows optimizing the computational resources as they can be focused on the processing of a set of selected regions. In the framework of mobile robotics navigation, this work proposes an artificial model where attention is deployed at the level of objects (visual landmarks) and where new processes for estimating bottom-up and top-down (target-based) saliency maps are employed. Bottom-up attention is implemented through a hierarchical process, whose final result is the perceptual grouping of the image content. The hierarchical grouping is applied using a Combinatorial Pyramid that represents each level of the hierarchy by a combinatorial map. The process takes into account both image regions (faces in the map) and edges (arcs in the map). Top-down attention searches for previously detected landmarks, enabling their re-detection when the robot presumes that it is revisiting a known location. Landmarks are described by a combinatorial submap; thus, this search is conducted through an error-tolerant submap isomorphism procedure.     

Perceptual organization based on illusory regions in infancy

Prior research indicates that, like adults, infants use enclosed regions to group elements. It is not clear whether infants or adults can use regions that have to be inferred from illusory contours to group elements. We examined whether 3- to 4-month-olds use illusory regions to group elements and generalize this organization to novel regions. Infants habituated to pairs of shapes in illusory vertical or horizontal regions subsequently discriminated, in novel regions, pairs of elements that had previously shared a region from pairs of elements that had been in different regions. A control group of infants, who had experienced the same stimuli except for the presence of illusory regions, failed to discriminate between within-region and between-region pairs of stimuli. These results reveal that (1) illusory regions can be used to group elements, (2) perceptual organization is sufficiently developed early in life for 3- to 4-month-olds to group on the basis of ecologically relevant illusory contours, and (3) such grouping in infancy generalizes to novel regions.     

Perceptual equivalence of acoustic cues in speech and nonspeech perception

Trading relations show that diverse acoustic consequences of minimal contrasts in speech are equivalent in perception of phonetic categories. This perceptual equivalence received stronger support from a recent finding that discrimination was differentially affected by the phonetic cooperation or conflict between two cues for the /slIt/-/splIt/contrast. Experiment 1 extended the trading relations and perceptual equivalence findings to the /sei/-/stei/contrast. With a more sensitive discrimination test, Experiment 2 found that cue equivalence is a characteristic of perceptual sensitivity to phonetic information. Using “sine-wave analogues” of the /sei/-/stei/stimuli, Experiment 3 showed that perceptual integration of the cues was phonetic, not psychoacoustic, in origin. Only subjects who perceived the sine-wave stimuli as “say” and “stay” showed a trading relation and perceptual equivalence; subjects who perceived them as nonspeech failed to integrate the two dimensions perceptually. Moreover, the pattern of differences between obtained and predicted discrimination was quite similar across the first two experiments and the “say”-“stay” group of Experiment 3, and suggested that phonetic perception was responsible even for better-than-predicted performance by these groups. Trading relations between speech cues, and the perceptual equivalence that underlies them, thus appear to derive specifically from perception of phonetic information.