Photorealism aftereffect

This study reports a novel visual aftereffect for photorealism judgments. Participants observed image sequences where a photograph was gradually transformed into an artificial image (a painting or a sketch). Their task was to choose the image that was the category boundary between the photograph and the artificial image among the frames of each image sequence. This task was performed before and after observing photographs or artificial images for 1 min. The chosen images were less photorealistic after the observation of artificial images, suggesting an aftereffect for photorealism judgments. However, observation of photographs did not induce an aftereffect. It is known that the observation of the norms for perceptual judgments (e.g., the prototypical face for facial judgments) does not induce aftereffects. Thus, these results suggest that photorealistic images serve as the norm for the perceptual judgment of photorealism. The human visual system may represent the photorealism of artificial images as a deviation from photorealistic images.     

Similarity and categorization: from vision to touch

Even though human perceptual development relies on combining multiple modalities, most categorization studies so far have focused on the visual modality. To better understand the mechanisms underlying multisensory categorization, we analyzed visual and haptic perceptual spaces and compared them with human categorization behavior. As stimuli we used a three-dimensional object space of complex, parametrically-defined objects. First, we gathered similarity ratings for all objects and analyzed the perceptual spaces of both modalities using multidimensional scaling analysis. Next, we performed three different categorization tasks which are representative of every-day learning scenarios: in a fully unconstrained task, objects were freely categorized, in a semi-constrained task, exactly three groups had to be created, whereas in a constrained task, participants received three prototype objects and had to assign all other objects accordingly. We found that the haptic modality was on par with the visual modality both in recovering the topology of the physical space and in solving the categorization tasks. We also found that within-category similarity was consistently higher than across-category similarity for all categorization tasks and thus show how perceptual spaces based on similarity can explain visual and haptic object categorization. Our results suggest that both modalities employ similar processes in forming categories of complex objects.     

Time course of perceptual grouping by color

Does perceptual grouping operate early or late in visual processing? One position is that the elements in perceptual layouts are grouped early in vision, by properties of the retinal image, before perceptual constancies have been determined. A second position is that perceptual grouping operates on a postconstancy representation, one that is available only after stereoscopic depth perception, lightness constancy, and amodal completion have occurred. The present experiments indicate that grouping can operate on both a preconstancy representation and a postconstancy representation. Perceptual grouping was based on retinal color similarity at short exposure durations and based on surface color similarity at long durations. These results permit an integration of the preconstancy and postconstancy positions with regard to grouping by color.     

Recognition memory for realistic synthetic faces

A series of experiments examined short-term recognition memory for trios of briefly presented, synthetic human faces derived from three real human faces. The stimuli were a graded series of faces, which differed by varying known amounts from the face of the average female. Faces based on each of the three real faces were transformed so as to lie along orthogonal axes in a 3-D face space. Experiment 1 showed that the synthetic faces' perceptual similarity structure strongly influenced recognition memory. Results were fit by a noisy exemplar model (NEMO) of perceptual recognition memory. The fits revealed thatrecognition memory was influenced both by the similarity of the probe to the series items and by the similarities among the series items themselves. Nonmetric multidimensional scaling (MDS) showed that the faces' perceptual representations largely preserved the 3-D space in which the face stimuli were arrayed. NEMO gave a better account of the results when similarity was defined as perceptual MDS similarity, rather than as the physical proximity of one face to another. Experiment 2 confirmed the importance of within-list homogeneity directly, without mediation of a model. We discuss the affinities and differences between visual memory for synthetic faces and memory for simpler stimuli.     

Intact visual discrimination of complex and feature-ambiguous stimuli in the absence of perirhinal cortex

The perirhinal cortex is known to be important for memory, but there has recently been interest in the possibility that it might also be involved in visual perceptual functions. In four experiments, we assessed visual discrimination ability and visual discrimination learning in severely amnesic patients with large medial temporal lobe lesions that included complete lesions of perirhinal cortex. Experiment 1 tested complex visual object perception. Experiments 2a and 2b tested in two different ways the ability to discriminate between feature-ambiguous images, which was reported to be impaired in monkeys with perirhinal lesions. Experiment 3 involved images that were successfully discriminated in Experiment 2a and asked patients to learn across 20 trials which of the images had been designated as "correct." Patients performed as well as controls in Experiments 1, 2a, and 2b, but one of the patients had difficulty in Experiment 3 when the task required remembering from trial to trial which image was "correct." These findings indicate that perirhinal cortex is not needed for visual perception across a wide range of visual perceptual tasks.     

视觉表象产生的大脑半球专门化效应

采用Kosslyn单侧视野速示技术, 以英文字母图片为学习材料, 通过三个实验考察了视觉表象产生的大脑半球专门化效应。实验一提出在两种类型的视觉表象产生任务中, 有两种截然不同的加工起作用, 但却不能直接证实这两种不同加工机制的存在。实验二和实验三则进一步证实了两种表象产生任务具有不同的认知加工机制, 并表现出不同的大脑半球专门化效应。上述研究表明: 大脑两半球均参与产生视觉心理表象, 但分工不同, 并表现出不同的单侧化效应: 大脑左半球通过运用类别空间关系产生表象更有效, 大脑右半球运用数量空间关系产生表象更有效。结果进一步拓展了Kosslyn关于视觉空间关系加工的大脑半球专门化观点。     

The time course of similarity effects in visual search

It is well established that visual search becomes harder when the similarity between target and distractors is increased and the similarity between distractors is decreased. However, in models of visual search, similarity is typically treated as a static, time-invariant property of the relation between objects. Data from other perceptual tasks (e.g., categorization) demonstrate that similarity is dynamic and changes as perceptual information is accumulated (Lamberts, 1998). In three visual search experiments, the time course of target-distractor similarity effects and distractor-distractor similarity effects was examined. A version of the extended generalized context model (EGCM; Lamberts, 1998) provided a good account of the time course of the observed similarity effects, supporting the notion that similarity in search is dynamic. Modeling also indicated that increasing distractor homogeneity influences both perceptual and decision processes by (respectively) increasing the rate at which stimulus features are processed and enabling strategic weighting of stimulus information.     

Fixation-dependent memory for natural scenes: an experimental test of scanpath theory

Many modern theories propose that perceptual information is represented by the sensorimotor activity elicited by the original stimulus. Scanpath theory (Noton & Stark, 1971) predicts that reinstating a sequence of eye fixations will help an observer recognize a previously seen image. However, the only studies to investigate this are correlational ones based on calculating scanpath similarity. We therefore describe a series of 5 experiments that constrain the fixations during encoding or recognition of images in order to manipulate scanpath similarity. Participants encoded a set of images and later had to recognize those that they had seen. They spontaneously selected regions that they had fixated during encoding (Experiment 1), and this was a predictor of recognition accuracy. Yoking the parts of the image available at recognition to the encoded scanpath led to better memory performance than randomly selected image regions (Experiment 2), and this could not be explained by the spatial distribution of locations (Experiment 3). However, there was no recognition advantage for re-viewing one's own fixations versus someone else's (Experiment 4) or for retaining their serial order (Experiment 5). Therefore, although it is beneficial to look at encoded regions, there is no evidence that scanpaths are stored or that scanpath recapitulation is functional in scene memory. This paradigm provides a controlled way of studying the integration of scene content, spatial structure, and oculomotor signals, with consequences for the perception, representation, and retrieval of visual information.     

Subjective value determines initial dominance in binocular rivalry

Does subjective reward value influence early visual perception? During binocular rivalry, one eye receives an image that is incompatible with the image the other eye receives. People consciously experience perceiving one image; the other image is suppressed from conscious awareness. We tested if subjective value functions as an endogenous influence (i.e., one internal to the perceiver) on dominance during rivalry. Images associated with rewards achieved initial perceptual dominance more often than images associated with cost (Study 1, Methods, Participants and procedures, Stimuli and presentation, Experimental counterbalancing conditions, Results, Study 2, Methods, Participants, Stimuli and presentation, Procedure, Results, Reports of letters v. numbers seen as initial percept, Reports of dot location, Study 3). Value facilitated perception of rewarding images but did not inhibit perception of costly images (Study 3). Additionally, when rewards benefited a disliked person, no bias in perceptual dominance was observed. Subjective value biased dominance despite accuracy incentives and was not explained by frequency of exposure, implicit learning, response bias, or task-specific accessibility. We discuss implications for the influence of motivated influences on perception, a phenomenon we call wishful seeing.     

Reliability and validity of the Leuven Perceptual Organization Screening Test (L‐POST)

Neuropsychological tests of visual perception mostly assess high‐level processes like object recognition. Object recognition, however, relies on distinct mid‐level processes of perceptual organization that are only implicitly tested in classical tests. Furthermore, the psychometric properties of the existing instruments are limited. To fill this gap, the Leuven perceptual organization screening test (L‐POST) was developed, in which a wide range of mid‐level phenomena are measured in 15 subtests. In this study, we evaluated reliability and validity of the L‐POST. Performance on the test is evaluated relative to a norm sample of more than 1,500 healthy control participants. Cronbach's alpha of the norm sample and test–retest correlations for 20 patients provide evidence for adequate reliability of L‐POST performance. The convergent and discriminant validity of the test was assessed in 40 brain‐damaged patients, whose performance on the L‐POST was compared with standard clinical tests of visual perception and other measures of cognitive function. The L‐POST showed high sensitivity to visual dysfunction and decreased performance was specific to visual problems. In conclusion, the L‐POST is a reliable and valid screening test for perceptual organization. It offers a useful online tool for researchers and clinicians to get a broader overview of the mid‐level processes that are preserved or disrupted in a given patient.     

Conventional naturalism: A perceptualist account of pictorial representation

This paper proposes that pictures are functional objects which figure in norm‐governed practices of usage yet whose specific function is to present the world as it looks to acculturated perceivers. Pictorial content presents the way the world looks to a subject's acculturated perceptual grasp. Hence, pictorial content needs to be explained in terms of a theory of perceptual content, but a novel theory which departs from the two‐stage sensation‐based approach to perception and the polarization between naturalism and conventionalism that it engenders. Following a diagnosis of this polarization, I invoke a novel theory of perception that explains perceptual content as conceptually articulated and determinate in character. I show that (1) pictures present content of the same distinctive determinate type as perceptual content; and that (2) pictures do so by invoking perceptual experience and perceptual processes that are of the same kind as those invoked by actual scenes. This perceptualist approach considers and explains the role of norms as well as of the nature of our visual processes, allowing us to allocate the insights of both conventionalism and naturalism to their proper theoretical roles.     

Human sensitivity to phase perturbations in natural images: a statistical framework

Fourier-phase information is important in determining the appearance of natural scenes, but the structure of natural-image phase spectra is highly complex and difficult to relate directly to human perceptual processes. This problem is addressed by extending previous investigations of human visual sensitivity to the randomisation and quantisation of Fourier phase in natural images. The salience of the image changes induced by these physical processes is shown to depend critically on the nature of the original phase spectrum of each image, and the processes of randomisation and quantisation are shown to be perceptually equivalent provided that they shift image phase components by the same average amount. These results are explained by assuming that the visual system is sensitive to those phase-domain image changes which also alter certain global higher-order image statistics. This assumption may be used to place constraints on the likely nature of cortical processing: mechanisms which correlate the outputs of a bank of relative-phase-sensitive units are found to be consistent with the patterns of sensitivity reported here.     

Familiarity,Priming, and Perception in Similarity Judgments

We present a novel way of accounting for similarity judgments. Our approach posits that similarity stems from three main sources—familiarity, priming, and inherent perceptual likeness. Here, we explore each of these constructs and demonstrate their individual and combined effectiveness in explaining similarity judgments. Using these three measures, our account of similarity explains ratings of simple, color‐based perceptual stimuli that display asymmetry effects, as well as more complicated perceptual stimuli with structural properties; more traditional approaches to similarity solve one or the other and have difficulty accounting for both. Overall, our work demonstrates the importance of each of these components of similarity in explaining similarity judgments, both individually and together, and suggests important implications for other similarity approaches.     

Improving Human‐Machine Cooperative Classification Via Cognitive Theories of Similarity

Acquiring perceptual expertise is slow and effortful. However, untrained novices can accurately make difficult classification decisions (e.g., skin‐lesion diagnosis) by reformulating the task as similarity judgment. Given a query image and a set of reference images, individuals are asked to select the best matching reference. When references are suitably chosen, the procedure yields an implicit classification of the query image. To optimize reference selection, we develop and evaluate a predictive model of similarity‐based choice. The model builds on existing psychological literature and accommodates stochastic, dynamic shifts of attention among visual feature dimensions. We perform a series of human experiments with two stimulus types (rectangles, faces) and nine classification tasks to validate the model and to demonstrate the model's potential to boost performance. Our system achieves high accuracy for participants who are naive as to the classification task, even when the classification task switches from trial to trial.     

Categorical perception of familiar objects

We report three experiments where the categorical perception of familiar, three-dimensional objects was investigated. A continuum of shape change between 15 pairs of objects was created and the images along the continuum were used as stimuli. In Experiment 1 participants were first required to discriminate pairs of images of objects that lay along the shape continuum. Then participants were asked to classify each morph-image into one of two pre-specified classes. We found evidence for categorical perception in some but not all of our object pairs. In Experiment 2 we varied the viewpoint of the objects in the discrimination task and found that effects of categorical perception generalized across changes in view. In Experiment 3 similarity ratings for each object pair were collected. These similarity scores correlated with the degree of perceptual categorization found for the object pairs. Our findings suggest that some familiar objects are perceived categorically and that categorical perception is closely tied to inter-object perceptual similarity.     

Modeling recognition memory using the similarity structure of natural input

The natural input memory (NIM) model is a new model for recognition memory that operates on natural visual input. A biologically informed perceptual preprocessing method takes local samples (eye fixations) from a natural image and translates these into a feature-vector representation. During recognition, the model compares incoming preprocessed natural input to stored representations. By complementing the recognition memory process with a perceptual front end, the NIM model is able to make predictions about memorability based directly on individual natural stimuli. We demonstrate that the NIM model is able to simulate experimentally obtained similarity ratings and recognition memory for individual stimuli (i.e., face images).     

Dissimilarity is used as evidence of category membership in multidimensional perceptual categorization: A test of the similarity–dissimilarity generalized context model

In exemplar models of categorization, the similarity between an exemplar and category members constitutes evidence that the exemplar belongs to the category. We test the possibility that the dissimilarity to members of competing categories also contributes to this evidence. Data were collected from two 2-dimensional perceptual categorization experiments, one with lines varying in orientation and length and the other with coloured patches varying in saturation and brightness. Model fits of the similarity–dissimilarity generalized context model were used to compare a model where only similarity was used with a model where both similarity and dissimilarity were used. For the majority of participants the similarity–dissimilarity model provided both a significantly better fit and better generalization, suggesting that people do also use dissimilarity as evidence.     

Extracting Low-Dimensional Psychological Representations from Convolutional Neural Networks

Convolutional neural networks (CNNs) are increasingly widely used in psychology and neuroscience to predict how human minds and brains respond to visual images. Typically, CNNs represent these images using thousands of features that are learned through extensive training on image datasets. This raises a question: How many of these features are really needed to model human behavior? Here, we attempt to estimate the number of dimensions in CNN representations that are required to capture human psychological representations in two ways: (1) directly, using human similarity judgments and (2) indirectly, in the context of categorization. In both cases, we find that low-dimensional projections of CNN representations are sufficient to predict human behavior. We show that these low-dimensional representations can be easily interpreted, providing further insight into how people represent visual information. A series of control studies indicate that these findings are not due to the size of the dataset we used and may be due to a high level of redundancy in the features appearing in CNN representations.     

Dissimilarity is used as evidence of category membership in multidimensional perceptual categorization: a test of the similarity-dissimilarity generalized context model

In exemplar models of categorization, the similarity between an exemplar and category members constitutes evidence that the exemplar belongs to the category. We test the possibility that the dissimilarity to members of competing categories also contributes to this evidence. Data were collected from two 2-dimensional perceptual categorization experiments, one with lines varying in orientation and length and the other with coloured patches varying in saturation and brightness. Model fits of the similarity-dissimilarity generalized context model were used to compare a model where only similarity was used with a model where both similarity and dissimilarity were used. For the majority of participants the similarity-dissimilarity model provided both a significantly better fit and better generalization, suggesting that people do also use dissimilarity as evidence.