Perceiving animacy from shape

Superordinate visual classification—for example, identifying an image as “animal,” “plant,” or “mineral”—is computationally challenging because radically different items (e.g., “octopus,” “dog”) must be grouped into a common class (“animal”). It is plausible that learning superordinate categories teaches us not only the membership of particular (familiar) items, but also general features that are shared across class members, aiding us in classifying novel (unfamiliar) items. Here, we investigated visual shape features associated with animate and inanimate classes. One group of participants viewed images of 75 unfamiliar and atypical items and provided separate ratings of how much each image looked like an animal, plant, and mineral. Results show systematic tradeoffs between the ratings, indicating a class-like organization of items. A second group rated each image in terms of 22 midlevel shape features (e.g., “symmetrical,” “curved”). The results confirm that superordinate classes are associated with particular shape features (e.g., “animals” generally have high “symmetry” ratings). Moreover, linear discriminant analysis based on the 22-D feature vectors predicts the perceived classes approximately as well as the ground truth classification. This suggests that a generic set of midlevel visual shape features forms the basis for superordinate classification of novel objects along the animacy continuum

Grouping principles in direct competition

AbstractWe (1) introduce a primed flanker task as an objective method to measure perceptual grouping, and (2) use it to directly compare the efficiency of different grouping cues in rapid visuomotor processing. In two experiments, centrally presented primes were succeeded by flanking targets with varying stimulus-onset asynchronies (SOAs). Primes and targets were grouped by the same or by different grouping cues (Exp. 1: brightness/shape, Exp. 2: brightness/size) and were consistent or inconsistent with respect to the required response. Subjective grouping strength was varied to identify its influence on overall response times, error rates, and priming effects, that served as a measure of visual feedforward processing. Our results show that stronger grouping in the targets enhanced overall response times while stronger grouping in the primes enhanced priming effects in motor responses. Also, we obtained differences between rapid visuomotor processing and the subjective impression with cues of brightness and shape but not with cues of brightness and size. Our findings establish the primed flanker task as an objective method to study the speeded visuomotor processing of grouping cues, making it a useful method for the comparative study of feedforward-transmitted base groupings (Roelfsema & Houtkamp, 2011)

Determining visual shape features for novel object classes

The visual representation of shape reduces a high-dimensional input into a smaller set of more informative features. These features can span a range of abstractions from shallow features based on statistical summaries of images, to deep features related to the generative causes of the shapes. Here we examined the depth of the visual system’s representation of shape by comparing human judgments of whether novel shapes appeared to belong to a common class with a range of models with different shape representations. Each shape class was based on a unique 2D base shape, formed by attaching parts of contours from different naturalistic shapes. We generated novel samples by transforming the base shape’s skeletal representation (Feldman and Singh, 2006) to produce new shapes with limbs that varied in length, width, spatial position, and orientation relative to the base shape. Multiple related classes were derived from each base shape using different distributions of parameter values. On each trial, observers judged whether the given target shape was in the same class as the given context shapes(either one or sixteen samples drawn from a particular shape class). Target shapes were samples taken from the same shape class as the context or one of the 5 related classes. Participants perform remarkably well given the ill-posed nature of the task. Models based on shallow features (Euclidean distance and shape area), and deep features (an ideal observer model with knowledge on the distribution of skeletal parts), were evaluated in terms of trial-by-trial consistency with the human data. In general, human responses indicated generalization beyond the context class and were best described by ideal and sub-optimal observer models suggesting that shape features for novel object classes are an abstract version of the underlying deep features

Adiabatic quantum simulations with driven superconducting qubits

We propose a quantum simulator based on driven superconducting qubits where the interactions are generated parametrically by a polychromatic magnetic flux modulation of a tunable bus element. Using a time-dependent Schrieffer-Wolff transformation, we analytically derive a multi-qubit Hamiltonian which features independently tunable $XX$ and $YY$-type interactions as well as local bias fields over a large parameter range. We demonstrate the adiabatic simulation of the ground state of a hydrogen molecule using two superconducting qubits and one tunable bus element. The time required to reach chemical accuracy lies in the few microsecond range and therefore could be implemented on currently available superconducting circuits. Further applications of this technique may also be found in the simulation of interacting spin systems.Comment: 11 pages, 6 figure

Identifying shape transformations from photographs of real objects

An important task of human visual cognition is to make inferences about properties of objects. One such property is an objects causal history: what happened to the object in its past (e.g., ´this paper has been folded). There is relatively little research on whether and how we make such inferences. We took photographs of objects from six different materials (´wax, ´aluminum foil, ´gold foil, ´chicken wire, ´putty, ´cardboard) transformed by one of four shape-altering transformations (´folded, ´bent, ´crumpled, ´twisted). By varying execution of transformation and viewpoint, we obtained 30 images of each material/transformation combination (720 images). We asked different groups of participants to: (1) name transformations and materials, (2) rate images with respect to the extent they belonged to each transformation or material class, and (3) classify images into the four transformation classes. Our results show that participants can infer transformations from object shape-with accuracy being modulated by object material. This inference of causal history from observed object shape shows that we can distinguish between intrinsic (material) and extrinsic (transformation) properties of the object. The separation of observed shape features by their causal origin (‘shape scission’) presumably involves both perceptual and cognitive abilities

Visual Processing in Rapid-Chase Systems: Image Processing, Attention, and Awareness

Visual stimuli can be classified so rapidly that their analysis may be based on a single sweep of feedforward processing through the visuomotor system. Behavioral criteria for feedforward processing can be evaluated in response priming tasks where speeded pointing or keypress responses are performed toward target stimuli which are preceded by prime stimuli. We apply this method to several classes of complex stimuli. (1) When participants classify natural images into animals or non-animals, the time course of their pointing responses indicates that prime and target signals remain strictly sequential throughout all processing stages, meeting stringent behavioral criteria for feedforward processing (rapid-chase criteria). (2) Such priming effects are boosted by selective visual attention for positions, shapes, and colors, in a way consistent with bottom-up enhancement of visuomotor processing, even when primes cannot be consciously identified. (3) Speeded processing of phobic images is observed in participants specifically fearful of spiders or snakes, suggesting enhancement of feedforward processing by long-term perceptual learning. (4) When the perceived brightness of primes in complex displays is altered by means of illumination or transparency illusions, priming effects in speeded keypress responses can systematically contradict subjective brightness judgments, such that one prime appears brighter than the other but activates motor responses as if it was darker. We propose that response priming captures the output of the first feedforward pass of visual signals through the visuomotor system, and that this output lacks some characteristic features of more elaborate, recurrent processing. This way, visuomotor measures may become dissociated from several aspects of conscious vision. We argue that “fast” visuomotor measures predominantly driven by feedforward processing should supplement “slow” psychophysical measures predominantly based on visual awareness

Experimental demonstration of the stability of Berry's phase for a spin-1/2 particle

The geometric phase has been proposed as a candidate for noise resilient coherent manipulation of fragile quantum systems. Since it is determined only by the path of the quantum state, the presence of noise fluctuations affects the geometric phase in a different way than the dynamical phase. We have experimentally tested the robustness of Berry's geometric phase for spin-1/2 particles in a cyclically varying magnetic field. Using trapped polarized ultra-cold neutrons it is demonstrated that the geometric phase contributions to dephasing due to adiabatic field fluctuations vanish for long evolution times.Comment: 4 pages, 4 figure