Lives as Collections of Strands: An Essay in Descriptive Psychology.

In this article I generalize the notion of multiple self-aspects to create a descriptive framework in which lives are partitioned into containers of activities called strands. Strands are nearly decomposable life modules, structured, stable, and concurrent longitudinal streams of extended duration whose momentary cross-sections constitute self-aspects. They are differentiated by five features: the person's role, the cast, the setting, norms and values, and habits and routines. Strands contain projects and episodes and are replete with narrative. Each strand is continuous (i.e., strands persist when a person moves between them), and for the most part strands are mutually asynchronous. From a first-person perspective, the strands are continuous and concurrent, but only one strand is in the foreground at a given time (i.e., transitions between strands are akin to a figure-ground reversal). Furthermore, a life is different from the sum of its strands: It is a nonlinear system that can take on configurations not predictable from a comprehensive description of the individual strands. Two such examples are the achievement of greatness despite severe handicaps and instances of extreme self-sacrifice. I also discuss the research potential of a proposed smartphone app called LifeMaps.

Questioning the automaticity of audiovisual correspondences.

An audiovisual correspondence (AVC) refers to an observer's seemingly arbitrary yet consistent matching of sensory features across the two modalities; for example, between an auditory pitch and visual size. Research on AVCs has frequently used a speeded classification procedure in which participants are asked to rapidly classify an image when it is either accompanied by a congruent or an incongruent sound (or vice versa). When, as is typically the case, classification is faster in the presence of a congruent stimulus, researchers have inferred that the AVC is automatic and bottom-up. Such an inference is incomplete because the procedure does not show that the AVC is not subject to top-down influences. To remedy this problem, we devised a procedure that allows us to assess the degree of "bottom-up-ness" and "top-down-ness" in the processing of an AVC. We did this in studies of AVCs between pitch and five visual features: size, height, spatial frequency, brightness, and angularity. We find that all the AVCs we studied involve both bottom-up and top-down processing, thus undermining the prevalent generalization that AVCs are automatic.

Competition between rhythmic and linguistic meaning revisited: the effect of task demands.

This paper revisits the conclusion of our previous work regarding the dominance of meaning in the competition between rhythmic parsing and linguistic parsing. We played five-note rhythm patterns in which each sound is a spoken word of a five-word sentence. We asked listeners to indicate the starting point of the rhythm while disregarding which word would normally be heard as the first word of the sentence. In four studies, we varied task demands by introducing differences in rhythm complexity, rhythm ambiguity, rhythm pairing, and semantic coherence. We found that task complexity affects the dominance of meaning. We therefore amend our previous conclusion: when processing resources are taxed, listeners do not always primarily attend to meaning; instead, they primarily attend to the aspect of the pattern (rhythm or meaning) that is more salient.

Perceiving the initial note: quantitative models of how listeners parse cyclical auditory patterns.

In this paper, we explore the rules followed by the auditory system in grouping temporal patterns. Imagine the following cyclical pattern (which we call an "auditory necklace"-AN for short-because those patterns are best visualized as beads arranged on a circle) consisting of notes (1s) and rests (0s): … 1110011011100110 …. It is perceived either as repeating 11100110 or as repeating 11011100. We devised a method to explore the temporal segmentation of ANs. In two experiments, while an AN was played, a circular array of icons appeared on the screen. At the time of each event (i.e., note or rest), one icon was highlighted; the highlight moved cyclically around the circular array. The participants were asked to click on the icon that corresponded to the note they perceived as the starting point, or clasp, of the AN. The best account of the segmentation of our ANs is based on Garner's (1974) run and gap principles. An important feature of our probabilistic model is the way in which it combines the effects of run length and gap length: additively. This result is an auditory analogue of Kubovy and van den Berg's (2008) discovery of the additivity of the effects of two visual grouping principles (proximity and similarity) conjointly applied to the same stimulus.

Dysrhythmia of timed movements in Parkinson's disease and freezing of gait.

A well-established motor timing paradigm, the Synchronization-Continuation Task (SCT), quantifies how accurately participants can time finger tapping to a rhythmic auditory beat (synchronization phase) then maintain this rhythm after the external auditory cue is extinguished, where performance depends on an internal representation of the beat (continuation phase). In this study, we investigated the hypothesis that Parkinson's disease (PD) patients with clinical symptoms of freezing of gait (FOG) exhibit exaggerated motor timing deficits. We predicted that dysrhythmia is exacerbated when finger tapping is stopped temporarily and then reinitiated under the guidance of an internal representation of the beat. Healthy controls and PD patients with and without FOG performed the SCT with and without the insertion of a 7-s cessation of motor tapping between synchronization and continuation phases. With no interruption between synchronization and continuation phases, PD patients, especially those with FOG, showed pronounced motor timing hastening at the slowest inter-stimulus intervals during the continuation phase. The introduction of a gap prior to the continuation phase had a beneficial effect for healthy controls and PD patients without FOG, although patients with FOG continued to show pronounced and persistent motor timing hastening. Ratings of freezing of gait severity across the entire sample of PD tracked closely with the magnitude of hastening during the continuation phase. These results suggest that PD is accompanied by a unique dysrhythmia of measured movements, with FOG reflecting a particularly pronounced disruption to internal rhythmic timing.

Competition between rhythmic and linguistic organization in a sentence-rhythm Stroop task.

We provide a test of Patel's [( 2003 ). Language, music, syntax and the brain. Nature Neuroscience, 6, 674-681] shared syntactic integration resources hypothesis by investigating the competition between determinants of rhythmic parsing and linguistic parsing using a sentence-rhythm Stroop task. We played five-note rhythm patterns in which each note is replaced with a spoken word of a five-word sentence and asked participants to indicate the starting point of the rhythm while they disregarded which word would normally be heard as the first word of the sentence. In Study 1, listeners completed the task in their native language. In Study 2, we investigated whether this competition is weakened if the sentences were in a listener's non-native language. In Study 3, we investigated how much language mastery is necessary to obtain the effects seen in Studies 1 and 2. We demonstrate that processing resources for rhythmic parsing and linguistic parsing overlap with one another, particularly when the task is demanding. We also show that the tendency for language to bias processing does not require deep knowledge of the language.

Deciphering the impact of cerebellar and basal ganglia dysfunction in accuracy and variability of motor timing.

Studies in motor timing have shown that the basal ganglia and cerebellum play an important role in temporal processing. Timing studies in Cerebellar/ataxic Disorders (CD) and Parkinson's disease (PD) patients contrast the roles of the cerebellum and basal ganglia in motor timing. Here, we used a synchronization-continuation task to compare accuracy and variability of motor timing during repetitive tapping. We compared data collected for the present study - from patients with CD and healthy controls - to data from a previous study with patients with PD. We asked participants to tap at Inter-stimulus Intervals (ISIs) of 250, 500, 1000, and 2000 ms. Using Linear Mixed Models (LMMs), we explored how ISI, Task Phase, and Diagnosis interacted to determine the (i) the accuracy and (ii) the variability of tapping. In our analysis of accuracy, we found evidence that during the synchronization phase, at ISI=250 ms, CD patients lagged 'behind the beat'; whereas our previous work has suggested that medicated PD patients hasten 'ahead of the beat'. In our analysis of variability, we observed that at ISIs below 1000 ms, CD patients showed greater variability in motor timing than the healthy controls, while PD patients showed less variability than CD patients and healthy controls during the synchronization phase at the 1000 ms ISI. These results highlight the differential performance on explicit motor timing between patients with disorders of the cerebellum and basal ganglia. Our results illustrate a novel approach to discerning cognitive control of motor timing.

A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure-ground organization.

In 1912, Max Wertheimer published his paper on phi motion, widely recognized as the start of Gestalt psychology. Because of its continued relevance in modern psychology, this centennial anniversary is an excellent opportunity to take stock of what Gestalt psychology has offered and how it has changed since its inception. We first introduce the key findings and ideas in the Berlin school of Gestalt psychology, and then briefly sketch its development, rise, and fall. Next, we discuss its empirical and conceptual problems, and indicate how they are addressed in contemporary research on perceptual grouping and figure-ground organization. In particular, we review the principles of grouping, both classical (e.g., proximity, similarity, common fate, good continuation, closure, symmetry, parallelism) and new (e.g., synchrony, common region, element and uniform connectedness), and their role in contour integration and completion. We then review classic and new image-based principles of figure-ground organization, how it is influenced by past experience and attention, and how it relates to shape and depth perception. After an integrated review of the neural mechanisms involved in contour grouping, border ownership, and figure-ground perception, we conclude by evaluating what modern vision science has offered compared to traditional Gestalt psychology, whether we can speak of a Gestalt revival, and where the remaining limitations and challenges lie. A better integration of this research tradition with the rest of vision science requires further progress regarding the conceptual and theoretical foundations of the Gestalt approach, which is the focus of a second review article.

Structural salience and the nonaccidentality of a Gestalt.

We perceive structure through a process of perceptual organization. Here we report a new perceptual organization phenomenon-the facilitation of visual grouping by global curvature. Observers viewed patterns that they perceived as organized into collections of curves. The patterns were perceptually ambiguous such that the perceived orientation of the patterns varied from trial to trial. When patterns were sufficiently dense and proximity was equated for the predominant perceptual alternatives, observers tended to perceive the organization with the greatest curvature. This effect is tantamount to visual grouping by maximal curvature and thus demonstrates an unprecedented effect of global structure on perceptual organization. We account for this result with a model that predicts the perceived organization of a pattern as function of its nonaccidentality, which we define as the probability that it could have occurred by chance. Our findings demonstrate a novel relationship between the geometry of a pattern and the visual salience of global structure.

Multistability, cross-modal binding and the additivity of conjoined grouping principles.

We present a sceptical view of multimodal multistability--drawing most of our examples from the relation between audition and vision. We begin by summarizing some of the principal ways in which audio-visual binding takes place. We review the evidence that unambiguous stimulation in one modality may affect the perception of a multistable stimulus in another modality. Cross-modal influences of one multistable stimulus on the multistability of another are different: they have occurred only in speech perception. We then argue that the strongest relation between perceptual organization in vision and perceptual organization in audition is likely to be by way of analogous Gestalt laws. We conclude with some general observations about multimodality.

Modeling accuracy and variability of motor timing in treated and untreated Parkinson's disease and healthy controls.

Parkinson's disease (PD) is characterized by difficulty with the timing of movements. Data collected using the synchronization-continuation paradigm, an established motor timing paradigm, have produced varying results but with most studies finding impairment. Some of this inconsistency comes from variation in the medication state tested, in the inter-stimulus intervals (ISI) selected, and in changeable focus on either the synchronization (tapping in time with a tone) or continuation (maintaining the rhythm in the absence of the tone) phase. We sought to re-visit the paradigm by testing across four groups of participants: healthy controls, medication naïve de novo PD patients, and treated PD patients both "on" and "off" dopaminergic medication. Four finger tapping intervals (ISI) were used: 250, 500, 1000, and 2000 ms. Categorical predictors (group, ISI, and phase) were used to predict accuracy and variability using a linear mixed model. Accuracy was defined as the relative error of a tap, and variability as the deviation of the participant's tap from group predicted relative error. Our primary finding is that the treated PD group (PD patients "on" and "off" dopaminergic therapy) showed a significantly different pattern of accuracy compared to the de novo group and the healthy controls at the 250-ms interval. At this interval, the treated PD patients performed "ahead" of the beat whilst the other groups performed "behind" the beat. We speculate that this "hastening" relates to the clinical phenomenon of motor festination. Across all groups, variability was smallest for both phases at the 500-ms interval, suggesting an innate preference for finger tapping within this range. Tapping variability for the two phases became increasingly divergent at the longer intervals, with worse performance in the continuation phase. The data suggest that patients with PD can be best discriminated from healthy controls on measures of motor timing accuracy, rather than variability.

Grouping by Regularity and the perception of illumination.

The purpose of this work is to describe how the visual system groups surfaces of unequal lightness under complex patterns of illumination. We propose that the Gestalt principle of Grouping by Regularity explains this process better than the more often cited principle of Grouping by Similarity. In our first experiment we demonstrate that in a perceptual organization task, pitting proximity against illumination gradients, discounting the illuminant was contingent upon the periodicity of the illuminant. Traditional theories of lightness constancy and discounting the illuminant (Rock, Nijhawan, Palmer, & Tudor, 1992) cannot account for such effects. Three more experiments show that grouping is affected more by local luminance ratios than constant reflectance ratios. We conclude from these findings that Grouping by Regularity is a powerful grouping principle that operates pre-constancy.

Causality and cross-modal integration.

Schutz and Lipscomb (2007) reported an audiovisual illusion in which the length of the gesture used to produce a sound altered the perception of that sound's duration. This contradicts the widely accepted claim that the auditory system generally dominates temporal tasks because of its superior temporal acuity. Here, in the first of 4 experiments, we show that impact gestures influence duration ratings of percussive but not sustained sounds. In the 2nd, we show that the illusion is present even if the percussive sound occurs up to 700 ms after the visible impact, but disappears if the percussive sound precedes the visible impact. In the 3rd experiment, we show that only the motion after the visible impact influences perceived tone duration. The 4th experiment (replacing the impact gestures with the written text long and short) suggests that the phenomenon is not due to response bias. Given that visual influence in this paradigm is dependent on the presence of an ecologically plausible audiovisual relationship, we conclude that cross-modal causality plays a key role in governing the integration of sensory information.

Visual determinants of a cross-modal illusion.

Contrary to the predictions of established theory, Schutz and Lipscomb (2007) have shown that visual information can influence the perceived duration of concurrent sounds. In the present study, we deconstruct the visual component of their illusion, showing that (1) cross-modal influence depends on visible cues signaling an impact event (namely, a sudden change of direction concurrent with tone onset) and (2) the illusion is controlled primarily by the duration of post-impact motion. Other aspects of the post-impact motion--distance traveled, velocity, acceleration, and the rate of its change (i.e., its derivative, jerk)--play a minor role, if any. Together, these results demonstrate that visual event duration can influence the perception of auditory event duration, but only when stimulus cues are sufficient to give rise to the perception of a causal cross-modal relationship. This refined understanding of the illusion's visual aspects is helpful in comprehending why it contrasts so markedly with previous research on cross-modal integration, demonstrating that vision does not appreciably influence auditory judgments of event duration (Walker & Scott, 1981).

The whole is equal to the sum of its parts: a probabilistic model of grouping by proximity and similarity in regular patterns.

The authors investigated whether the gestalt grouping principles can be quantified and whether the conjoint effects of two grouping principles operating at the same time on the same stimuli differ from the sum of their individual effects. After reviewing earlier attempts to discover how grouping principles interact, they developed a probabilistic model of grouping by proximity, which allows measurement of strength on a ratio scale. Then, in 3 experiments using dot lattices, they showed that the strength of the conjoint effect of 2 grouping principles--grouping by proximity and grouping by similarity--is equal to the sum of their separate effects. They propose a physiologically plausible model of this law.

Dissociation of early evoked cortical activity in perceptual grouping.

Perceptual grouping is a multi-stage process, irreducible to a single mechanism localized anatomically or chronometrically. To understand how various grouping mechanisms interact, we combined a phenomenological report paradigm with high-density event-related potential (ERP) measurements, using a 256-channel electrode array. We varied the relative salience of competing perceptual organizations in multi-stable dot lattices and asked observers to report perceived groupings. The ability to discriminate groupings (the grouping sensitivity) was positively correlated with the amplitude of the earliest ERP peak C1 (about 60 ms after stimulus onset) over the middle occipital area. This early activity is believed to reflect spontaneous feed-forward processes preceding perceptual awareness. Grouping sensitivity was negatively correlated with the amplitude of the next peak P1 (about 110 ms), which is believed to reflect lateral and feedback interactions associated with perceptual awareness and attention. This dissociation between C1 and P1 activity implies that the recruitment of fast, spontaneous mechanisms for grouping leads to high grouping sensitivity. Observers who fail to recruit these mechanisms are trying to compensate by using later mechanisms, which depend less on stimulus properties such as proximity.

The economics of motion perception and invariants of visual sensitivity.

Neural systems face the challenge of optimizing their performance with limited resources, just as economic systems do. Here, we use tools of neoclassical economic theory to explore how a frugal visual system should use a limited number of neurons to optimize perception of motion. The theory prescribes that vision should allocate its resources to different conditions of stimulation according to the degree of balance between measurement uncertainties and stimulus uncertainties. We find that human vision approximately follows the optimal prescription. The equilibrium theory explains why human visual sensitivity is distributed the way it is and why qualitatively different regimes of apparent motion are observed at different speeds. The theory offers a new normative framework for understanding the mechanisms of visual sensitivity at the threshold of visibility and above the threshold and predicts large-scale changes in visual sensitivity in response to changes in the statistics of stimulation and system goals.

The lawful perception of apparent motion.

Visual apparent motion is the experience of motion from the successive stimulation of separate spatial locations. How spatial and temporal distances interact to determine the strength of apparent motion has been controversial. Some studies report space-time coupling: If we increase spatial or temporal distance between successive stimuli, we must also increase the other distance between them to maintain a constant strength of apparent motion (Korte's third law of motion). Other studies report space-time tradeoff: If we increase one of these distances, we must decrease the other to maintain a constant strength of apparent motion. In this article, we resolve the controversy. Starting from a normative theory of motion measurement and data on human spatiotemporal sensitivity, we conjecture that both coupling and tradeoff should occur, but at different speeds. We confirm the prediction in two experiments, using suprathreshold multistable apparent-motion displays called motion lattices. Our results show a smooth transition between the tradeoff and coupling as a function of speed: Tradeoff occurs at low speeds and coupling occurs at high speeds. From our data, we reconstruct the suprathreshold equivalence contours that are analogous to isosensitivity contours obtained at the threshold of visibility.

On the surprising salience of curvature in grouping by proximity.

The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the dot lattices used to study grouping by proximity, except that only one of the potential organizations is rectilinear; the others are curvilinear. The authors used the method of M. Kubovy and J. Wagemans (1995) to study grouping by proximity in DSGs. They found that in the competition between the most likely organizations, one rectilinear and the other curvilinear, the latter is more salient. This phenomenon cannot be explained by contemporary accounts of grouping by proximity or contour integration.

Stability and change in perception: spatial organization in temporal context.

Perceptual multistability has often been explained using the concepts of adaptation and hysteresis. In this paper we show that effects that would typically be accounted for by adaptation and hysteresis can be explained without assuming the existence of dedicated mechanisms for adaptation and hysteresis. Instead, our data suggest that perceptual multistability reveals lasting states of the visual system rather than changes in the system caused by stimulation. We presented observers with two successive multistable stimuli and found that the probability that they saw the favored organization in the first stimulus was inversely related to the probability that they saw the same organization in the second. This pattern of negative contingency is orientation-tuned and occurs no matter whether the observer had or had not seen the favored organization in the first stimulus. This adaptation-like effect of negative contingency combines multiplicatively with a hysteresis-like effect that increases the likelihood of the just-perceived organization. Both effects are consistent with a probabilistic model in which perception depends on an orientation-tuned intrinsic bias that slowly (and stochastically) changes its orientation tuning over time.