A hypothesis connecting visual pattern recognition and apparent motion

The study improves upon a previous hypothesis which claims a connection between the existence of a certain visual apparentmotion effect and the capacity of the visual system to recognize, in a very general sense, objects that have undergone certain transformations. In the present work a sharper hypothesis is developed by making use of the notion of visual recognition defined with respect to a fixed local Lie transformation group G. Considering the apparent-motion effect between an object A and some transform (A) of A as arising from the action of a certain 1-parameter family of transformations generated by the visual system, this hypothesis asserts that if the 1-parameter family lies entirely within G, then the visual system is capable of recognizing with respect to G the transformed object (A) as the original object A.     

Invariance of visual operations at the level of receptive fields

The brain is able to maintain a stable perception although the visual stimuli vary substantially on the retina due to geometric transformations and lighting variations in the environment. This paper presents a theory for achieving basic invariance properties already at the level of receptive fields. Specifically, the presented framework comprises (i) local scaling transformations caused by objects of different size and at different distances to the observer, (ii) locally linearized image deformations caused by variations in the viewing direction in relation to the object, (iii) locally linearized relative motions between the object and the observer and (iv) local multiplicative intensity transformations caused by illumination variations. The receptive field model can be derived by necessity from symmetry properties of the environment and leads to predictions about receptive field profiles in good agreement with receptive field profiles measured by cell recordings in mammalian vision. Indeed, the receptive field profiles in the retina, LGN and V1 are close to ideal to what is motivated by the idealized requirements. By complementing receptive field measurements with selection mechanisms over the parameters in the receptive field families, it is shown how true invariance of receptive field responses can be obtained under scaling transformations, affine transformations and Galilean transformations. Thereby, the framework provides a mathematically well-founded and biologically plausible model for how basic invariance properties can be achieved already at the level of receptive fields and support invariant recognition of objects and events under variations in viewpoint, retinal size, object motion and illumination. The theory can explain the different shapes of receptive field profiles found in biological vision, which are tuned to different sizes and orientations in the image domain as well as to different image velocities in space-time, from a requirement that the visual system should be invariant to the natural types of image transformations that occur in its environment.     

The acheulean handaxe: More like a bird's song than a beatles' tune?

The goal of this paper is to provoke debate about the nature of an iconic artifact—the Acheulean handaxe. Specifically, we want to initiate a conversation about whether or not they are cultural objects. The vast majority of archeologists assume that the behaviors involved in the production of handaxes were acquired by social learning and that handaxes are therefore cultural. We will argue that this assumption is not warranted on the basis of the available evidence and that an alternative hypothesis should be given serious consideration. This alternative hypothesis is that the form of Acheulean handaxes was at least partly under genetic control.     

Researchers Keep Rejecting Grandmother Cells after Running the Wrong Experiments: The Issue Is How Familiar Stimuli Are Identified

There is widespread agreement in neuroscience and psychology that the visual system identifies objects and faces based on a pattern of activation over many neurons, each neuron being involved in representing many different categories. The hypothesis that the visual system includes finely tuned neurons for specific objects or faces for the sake of identification, so‐called “grandmother cells”, is widely rejected. Here it is argued that the rejection of grandmother cells is premature. Grandmother cells constitute a hypothesis of how familiar visual categories are identified, but the primary evidence against this hypothesis comes from studies that have failed to observe neurons that selectively respond to unfamiliar stimuli. These findings are reviewed and it is shown that they are irrelevant. Neuroscientists need to better understand existing models of face and object identification that include grandmother cells and then compare the selectivity of these units with single neurons responding to stimuli that can be identified.     

Visual apparent motion and some preferred paths in the rotation group SO(3)

The sequential presentation of two distinct stimulus objects to the visual system will, under certain conditions, induce an apparentmotion effect, called beta motion, in which the first object appears to smoothly transform into the second. This study is concerned with the kinds of paths selected by the visual system in effecting beta motion in which the metric structure of the object is preserved throughout. Two schemes are advanced according to which the visual system might operate. The first concentrates upon the manifold M in which the object appears to transform and the second upon the group G of transformations of M onto itself in which the particular transformation describing this motion lie. Under the identification of M with the 2-sphere S ², each scheme specifies the action-minimizing curves in the rotation group SO(3) for a particular “natural” Riemannian metric. An experiment is described in which a determination is made of the actual paths taken by an object under-going various rigid-motion beta motions. The results obtained indicate that the visual system behaves more in accordance with the second scheme than with the first. A generalization of this result is briefly discussed.     

Dependence of the threshold of sinusoidal grating displacement on its spatial frequency characteristics

The threshold of detection of sinusoidal grating displacement was studied under conditions of the absence of apparent movement. It was shown that the threshold rises with the pattern size and depends on the number of grating cycles at a constant stimulus magnitude. The stimulus size in 2–3 periods is optimal for its localization. The results suggest that objects in the visual field are localized by mechanisms tuned to a certain spatial frequency and selective to a certain image size. The size of the analyzed part of the visual field requires respective frequency tuning of the mechanism.     

Recognition of partly occluded patterns: a neural network model

 Human beings are often able to read a letter or word partly occluded by contaminating ink stains. However, if the stains are completely erased and the occluded areas of the letter are changed to white, we usually have difficulty in reading the letter. In this article I propose a hypothesis explaining why a pattern is easier to recognize when it is occluded by visible objects than by invisible opaque objects. A neural network model is constructed based on this hypothesis. The visual system extracts various visual features from the input pattern and then attempts to recognize it. If the occluding objects are not visible, the visual system will have difficulty in distinguishing which features are relevant to the original pattern and which are newly generated by the occlusion. If the occluding objects are visible, however, the visual system can easily discriminate between relevant and irrelevant features and recognize the occluded pattern correctly. The proposed model is an extended version of the neocognitron model. The activity of the feature-extracting cells whose receptive fields cover the occluding objects is suppressed in an early stage of the hierarchical network. Since the irrelevant features generated by the occlusion are thus eliminated, the model can recognize occluded patterns correctly, provided the occlusion is not so large as to prevent recognition even by human beings. Received: 21 February 2000 / Accepted in revised form: 11 September 2000     

Generalization of learning by synchronous waves: from perceptual organization to invariant organization

From a few presentations of an object, perceptual systems are able to extract invariant properties such that novel presentations are immediately recognized. This may be enabled by inferring the set of all representations equivalent under certain transformations. We implemented this principle in a neurodynamic model that stores activity patterns representing transformed versions of the same object in a distributed fashion within maps, such that translation across the map corresponds to the relevant transformation. When a pattern on the map is activated, this causes activity to spread out as a wave across the map, activating all the transformed versions represented. Computational studies illustrate the efficacy of the proposed mechanism. The model rapidly learns and successfully recognizes rotated and scaled versions of a visual representation from a few prior presentations. For topographical maps such as primary visual cortex, the mechanism simultaneously represents identity and variation of visual percepts whose features change through time.     

THE RELATION BETWEEN VISUAL ACUITY AND ILLUMINATION

1. An apparatus for measuring the visual acuity of the eye at different illuminations is described. The test object is continuously variable in size and is presented at a fixed distance from the eye in the center of a 30° field. Observation of the field is through an artificial pupil. The maximum intensity obtainable is more than enough to cover the complete physiological range for the eye with white light though only 110 watts are consumed by the source. Means for varying the intensity over a range of 1:10¹⁰ in small steps are provided. 2. The relation of visual acuity and illumination for two trained observers was measured, using two different types of test object, a broken circle and a grating. The measurements with both test objects show a break at a visual acuity of 0.16, all values below that being mediated by the rods and those above by the cones. The grating gives higher visual acuities at intensities less than about 30 photons and lower visual acuities above that. The maximum visual acuity attainable with the grating under the same conditions is about 30 per cent lower than that with the C. It is shown that the limiting factor in the resolution of the eye for the grating is the diameter of the pupil when it is less than 2.3 mm. and the size of the central cones when the pupil is larger than that. The value of the diameter of the cone derived on that basis from the visual acuity data agrees with that derived from direct cone count in a unit of area. 3. The data for the cones made with both test objects are adequately described by one and the same form of the stationary state equation derived by Hecht for the photoreceptor system. This fact, together with certain considerations about the difference in the nature of the two test objects with regard to the resolvable area, leads to the conclusion that detail perception is a function of a distance rather than an area. All the data for the rods can likewise be described by another variety of the same equation, although the data are too fragmentary to make the choice of the form as certain as might be desired.     

Bedamini Male Initiation and Marriage as Transformation Sequences

ABSTRACT

This essay focuses on how certain social relations among the Bedamini in Papua New Guinea are given their form through ritual at selected moments of the life cycle when relational transformations occur. Ritualised moments in Bedamini male initiation and symbolic bride capture are described as a dynamic agency that changes the existential conditions of persons in non-ritual reality. At those important ritual moments, the direct presence of the agents is required, while relations between them are mediated by acts, objects and moods. The effect intended is the formation, or reformation, of a relational field. Male initiation and marriage are consecutive parts of a sequence of transformations beyond its constituent moments, as initiation functions as a prerequisite to marriage.     

Evaluation of disruptive camouflage of avian cup‐nests

Parent birds employ various strategies to protect their offspring against nest predators. Two well‐researched anti‐nest‐predation strategies involve visual concealment of the nest by way of parental camouflage and egg camouflage. By contrast, camouflage of nest structures is relatively under‐researched, particularly in the case of cup‐nests in trees and bushes. We explored how birds camouflage cup‐nests in nature. Specifically, we tested Hansell’s hypothesis that birds use externally applied pale and white objects such as spider cocoons and lichens to achieve cup‐nest camouflage. To test Hansell’s hypothesis, three complementary experiments were performed: (1) an in situ nest predation experiment; (2) a photo‐based visual search experiment; and (3) contrast analyses using PAT‐GEOM software in IMAGEJ. White paper and chalk spots were used to mimic white objects used by birds in nature. Whereas predation rates in Experiment 1 were not affected by white spots, location rates in Experiment 2 were lower for natural nests with white spots than without white spots. Experiment 3 demonstrated that white spots significantly increased the contrast between different visual elements of nests. It was concluded that white objects can potentially camouflage nests against some nest predators, and that any improved camouflage was probably achieved via disruptive camouflage.     

Common Visual Preference for Curved Contours in Humans and Great Apes

Among the visual preferences that guide many everyday activities and decisions, from consumer choices to social judgment, preference for curved over sharp-angled contours is commonly thought to have played an adaptive role throughout human evolution, favoring the avoidance of potentially harmful objects. However, because nonhuman primates also exhibit preferences for certain visual qualities, it is conceivable that humans’ preference for curved contours is grounded on perceptual and cognitive mechanisms shared with extant nonhuman primate species. Here we aimed to determine whether nonhuman great apes and humans share a visual preference for curved over sharp-angled contours using a 2-alternative forced choice experimental paradigm under comparable conditions. Our results revealed that the human group and the great ape group indeed share a common preference for curved over sharp-angled contours, but that they differ in the manner and magnitude with which this preference is expressed behaviorally. These results suggest that humans’ visual preference for curved objects evolved from earlier primate species’ visual preferences, and that during this process it became stronger, but also more susceptible to the influence of higher cognitive processes and preference for other visual features.     

When Kinesthesia Becomes Visual: A Theoretical Justification for Executing Motor Tasks in Visual Space

Several experimental studies in the literature have shown that even when performing purely kinesthetic tasks, such as reaching for a kinesthetically felt target with a hidden hand, the brain reconstructs a visual representation of the movement. In our previous studies, however, we did not observe any role of a visual representation of the movement in a purely kinesthetic task. This apparent contradiction could be related to a fundamental difference between the studied tasks. In our study subjects used the same hand to both feel the target and to perform the movement, whereas in most other studies, pointing to a kinesthetic target consisted of pointing with one hand to the finger of the other, or to some other body part. We hypothesize, therefore, that it is the necessity of performing inter-limb transformations that induces a visual representation of purely kinesthetic tasks. To test this hypothesis we asked subjects to perform the same purely kinesthetic task in two conditions: INTRA and INTER. In the former they used the right hand to both perceive the target and to reproduce its orientation. In the latter, subjects perceived the target with the left hand and responded with the right. To quantify the use of a visual representation of the movement we measured deviations induced by an imperceptible conflict that was generated between visual and kinesthetic reference frames. Our hypothesis was confirmed by the observed deviations of responses due to the conflict in the INTER, but not in the INTRA, condition. To reconcile these observations with recent theories of sensori-motor integration based on maximum likelihood estimation, we propose here a new model formulation that explicitly considers the effects of covariance between sensory signals that are directly available and internal representations that are ‘reconstructed’ from those inputs through sensori-motor transformations.     

A simple strategy for detecting moving objects during locomotion revealed by animal-robot interactions

An important role of visual systems is to detect nearby predators, prey, and potential mates, which may be distinguished in part by their motion. When an animal is at rest, an object moving in any direction may easily be detected by motion-sensitive visual circuits. During locomotion, however, this strategy is compromised because the observer must detect a moving object within the pattern of optic flow created by its own motion through the stationary background. However, objects that move creating back-to-front (regressive) motion may be unambiguously distinguished from stationary objects because forward locomotion creates only front-to-back (progressive) optic flow. Thus, moving animals should exhibit an enhanced sensitivity to regressively moving objects. We explicitly tested this hypothesis by constructing a simple fly-sized robot that was programmed to interact with a real fly. Our measurements indicate that whereas walking female flies freeze in response to a regressively moving object, they ignore a progressively moving one. Regressive motion salience also explains observations of behaviors exhibited by pairs of walking flies. Because the assumptions underlying the regressive motion salience hypothesis are general, we suspect that the behavior we have observed in Drosophila may be widespread among eyed, motile organisms.     

Masticatory stress, orbital orientation and the evolution of the primate postorbital bar

A postorbital bar is one of a suite of derived features which distinguishes basal primates from their putative sister taxon, plesiadapiforms. Two hypotheses have been put forward to explain postorbital bar development and variation in circumorbital form: the facial torsion model and visual predation hypothesis. To test the facial torsion model, we employ strain data on circumorbital and mandibular loading patterns in representative primates with a postorbital bar and masticatory apparatus similar to basal primates. To examine the visual predation hypothesis, we employ metric data on orbit orientation in Paleocene and Eocene primates, as well as several clades of visual predators and foragers that vary interspecifically in postorbital bar formation.A comparison of galago circumorbital and mandibular peak strains during powerful mastication demonstrates that circumorbital strains are quite low. This indicates that, as in anthropoids, the strepsirhine circumorbital region is excessively overbuilt for countering routine masticatory loads. The fact that circumorbital peak-strain levels are uniformly low in both primate suborders undermines any model which posits that masticatory stresses are determinants of circumorbital form, function and evolution. This is interpreted to mean that sufficient cortical bone must exist to prevent structural failure due to non-masticatory traumatic forces. Preliminary data also indicate that the difference between circumorbital and mandibular strains is greater in larger taxa.Comparative analyses of several extant analogs suggest that the postorbital bar apparently provides rigidity to the lateral orbital margins to ensure a high level of visual acuity during chewing and biting. The origin of the primate postorbital bar is linked to changes in orbital convergence and frontation at smaller sizes due to nocturnal visual predation and increased encephalization. By incorporating in vivo and fossil data, we reformulate the visual predation hypothesis of primate origins and thus offer new insights into major adaptive transformations in the primate skull.     

Visual monitoring of threatening objects by captive tamarins (Saguinus labiatus)

Captive social groups of red-bellied tamarins (Saguinus labiatus) were observed in the presence of threatening, inanimate objects. The tamarins monitored the stimuli over the course of the 20-minute trials by conducting brief, periodic visual checks of the objects. The average number of checks per subject per trial was stable both across trials and between groups, and individual differences in rates varied relatively little around the group means. These data generate the hypothesis that there is a species-typical execution of vigilance in the presence of mildly threatening objects. This execution takes the form of brief visual inspections of the stimulus, usually by one tamarin at a time, at a fairly consistent rate. The discussion of the data takes place in the context of the behavioral ecology of callitrichid species.     

Stimulus dependency of object-evoked responses in human visual cortex: an inverse problem for category specificity

Many studies have linked the processing of different object categories to specific event-related potentials (ERPs) such as the face-specific N170. Despite reports showing that object-related ERPs are influenced by visual stimulus features, there is consensus that these components primarily reflect categorical aspects of the stimuli. Here, we re-investigated this idea by systematically measuring the effects of visual feature manipulations on ERP responses elicited by both structure-from-motion (SFM)-defined and luminance-defined object stimuli. SFM objects elicited a novel component at 200-250 ms (N250) over parietal and posterior temporal sites. We found, however, that the N250 amplitude was unaffected by restructuring SFM stimuli into meaningless objects based on identical visual cues. This suggests that this N250 peak was not uniquely linked to categorical aspects of the objects, but is strongly determined by visual stimulus features. We provide strong support for this hypothesis by parametrically manipulating the depth range of both SFM- and luminance-defined object stimuli and showing that the N250 evoked by SFM stimuli as well as the well-known N170 to static faces were sensitive to this manipulation. Importantly, this effect could not be attributed to compromised object categorization in low depth stimuli, confirming a strong impact of visual stimulus features on object-related ERP signals. As ERP components linked with visual categorical object perception are likely determined by multiple stimulus features, this creates an interesting inverse problem when deriving specific perceptual processes from variations in ERP components.     

Perceptual Centering Effects in Body Orientation

This study mathematically characterizes the results of DiZio and Lackner (Percept Psychphys 39(1): 39–46) on the perception of self-orientation during circular vection induced by an optokinetic stimulus. Using the hypothesis of perceptual centering, it is shown that five basic centering transformations can logically account for the full range of illusions reported by the subjects. All five of these transformations center the perceived orientations of body components, the rotating disk, and gravity : two align the perceived visual and inertial rotation axes, one centers the perceived axis of visual rotation in front of the head, and two straighten the perceived neck angle. These transformations generate a mathematical semigroup. Application of the semigroup to an actual stimulus condition generates an orbit of predicted illusions. The semigroup analysis of perceptual centering predicts all of the illusions observed in the experiments of DiZio and Lackner (Percept Psychphys 39(1): 39–46). Moreover, the structure of perceptual centering (1) provides a logical explanation for the occurrence of those misperceptions; and (2) predicts the complete set of perceptions that are expected to occur in a larger sample. In addition, our analysis predicts illusions in experimental conditions not yet investigated     

Subcortical discrimination of unperceived objects during binocular rivalry

Rapid identification of behaviorally relevant objects is important for survival. In humans, the neural computations for visually discriminating complex objects involve inferior temporal cortex (IT). However, less detailed but faster form processing may also occur in a phylogenetically older subcortical visual system that terminates in the amygdala. We used binocular rivalry to present stimuli without conscious awareness, thereby eliminating the IT object representation and isolating subcortical visual input to the amygdala. Functional magnetic resonance imaging revealed significant brain activation in the left amygdala but not in object-selective IT in response to unperceived fearful faces compared to unperceived nonface objects. These findings indicate that, for certain behaviorally relevant stimuli, a high-level cortical representation in IT is not required for object discrimination in the amygdala.