Effect of static visual acuity on dynamic visual acuity: a pilot study

The aim of this pilot study was to evaluate whether dynamic visual acuity changes with or without refractive correction. 42 healthy enrolled subjects with normal vision were divided into two age-matched groups. In Group A, dynamic visual acuity was measured first with the refractive error fully corrected and then without. In Group B, dynamic visual acuity measurements were taken in the reverse order of that performed by Group A. The measurements were binocularly performed five times using free-head viewing after dynamic visual acuity values were stable. Significant changes in dynamic visual acuity (static visual acuity 20/20 vs 12/20) were observed in both Group A (171.6 +/- 36.0 deg./sec. vs 151.8 +/- 39.6 deg./sec., Wilcoxon test, p < .001) and Group B (169.8 +/- 30.0 deg./sec. vs 151.2 +/- 36.0 deg./sec., Wilcoxon test, p < .001). The interaction was significant (F1.20 = 8.12, p = .009). These results indicated that refractive correction affected dynamic visual acuity.     

Temporal factorisation: A unifying principle for dynamics of the world and of mental states

Dynamics play a major role in many phenomena, addressed in a variety of disciplines. This paper contributes to the identification of common principles underlying approaches to dynamics used within a variety of cognitive and noncognitive disciplines, such as Cognitive Science, Physics, Mathematics, Chemistry, Computer Science and Biology. More specifically, as a central, unifying principle, the temporal factorisation principle is introduced, formalised and illustrated. This principle expresses, that every temporal relationship of the form ‘past pattern implies future pattern’ can be factorised into a relationship of the form ‘past pattern implies present state’ and a relationship of the form ‘present state implies future pattern’. To enable this, for every ‘past pattern implies future pattern’ relationship, the principle postulates the existence of certain mediating state properties in the present state. It provides a conceptual framework which unifies various approaches to dynamics within a variety of disciplines. In particular, it is shown how the principle can be applied in the case of cognitive states of agents.     

Visual acuity improvement following fading and feedback training—II. Relationship to changes in refractive error

The present study evaluated the effects of behavioral training on visual acuity and refractive error in myopic adults. Twenty volunteers were matched on the basis of refractive error and one member of each matched pair was randomly assigned to either Fading and Feedback training or a no-treatment control condition. Visual acuity was measured with both recognition and resolution measures. Refractive error was measured subjectively using the LaserSpec optometer, and objectively by two retinoscopic examinations performed by an ophthalmologist with and without cycloplegia. The results indicated significant increases in recognition visual acuity, but not resolution visual acuity for trained subjects compared to the no-treatment controls. Trained subjects did not show improvement in refractive error on any measure, and refractive error changes were not correlated with changes in either measure of visual acuity. These data suggest that the visual acuity improvements typically found with behavioral training are not associated with changes in refractive error.     

Temporal factorisation: Realisation of mediating state properties for dynamics

Temporal factorisation is a principle underlying approaches to dynamics used within many disciplines. According to this principle any temporal relationship of the form ‘past pattern implies future pattern’ can be factorised into a relationship of the form ‘past pattern implies present state’ and a relationship of the form ‘present state implies future pattern’. To enable this, the principle postulates the existence of certain mediating state properties in the present state. In this paper the question is addressed whether and how a postulated mediating state property relates to other state properties in the (present) state in which they occur. In particular, the situation is analysed that realisers exist: other state properties or combinations thereof that co-occur with the mediating state property in states. This analysis provides a conceptual framework covering various concepts and themes that usually are considered totally different and unrelated, such as, the notion of differential equation in Mathematics, the notions of transition system and rule-based system in Computer Science, Cognitive Science and Artificial Intelligence, and the notion of reduction in Cognitive Science and Philosophy of Science.     

The virtual haptic display: A device for exploring 2-D virtual shapes in the tactile modality

In order to understand better the processes involved in the perception of shape through touch, someelement of control is required over the nature of the shape presented to the hand and the presentation timing. To that end, we have developed a cost-effective, computer-controlled apparatus for presenting haptic stimuli using active touch, known as a virtual haptic display (VHD). The operational principle behind this device is that it translates black and white visual images into topographic, 2-D taxel (tactile pixel) arrays, along the same principle using in Braille letters. These taxels are either elevated or depressed at any one time representing white and black pixel colors of the visual image, respectively. To feel the taxels, the participant places their fingers onto a carriage which can be moved over the surface of the device to reveal a virtual shape. We conducted two experiments and the results show that untrained participants are able to recognize different, simple and complex, shapes using this apparatus. The VHD apparatus is therefore ideal at presenting 2-Dshapes through touch alone. Moreover,this device and its supporting software can also be used for presenting computer-controlled stimuli in cross-modal experiments.     

Rethinking perceptual organization: The role of uniform connectedness

A principle of perceptual organization, calleduniform connectedness (UC), is described, and a theoretical approach to perceptual organization is proposed in which this principle plays a fundamental role. The principle of UC states that closed regions of homogeneous properties—such as lightness, chromatic color, texture, and so forth—tend to be perceived initially as single units. We demonstrate its effects and show that they occur even when opposed by powerful grouping principles such as proximity and similarity. We argue that UC cannot be reduced to such grouping principles, because it is not a form of grouping at all. We then propose a theoretical framework within which UC accounts for the initial (orentry level) organization of the visual field into primitive units. Classical principles of grouping operate after UC, creating superordinate units consisting of two or more basic-level units. Parsing processes also operate after UC, dividing basic-level units into subordinate parts. UC in the retinal image is proposed to be a necessary, but not a sufficient, condition for unit formation, since connected elements on the retina that are perceived to lie in separate depth planes fail to be perceived as units. This fact, together with other evidence that the Gestalt principles of grouping are based onperceived (rather than retinal) relations, suggests that the organization of visual stimulation into UC objects is ultimately achieved within a relatively late, postconstancy representation of environmental surfaces. The implications of this possibility are discussed in light of present theories of visual perception.     

Peripheral visual acuity and refractive error: Evidence for “two visual systems”?

Experiments conducted in two independent laboratories indicate that the correction of refractive errors does not improve peripheral visual acuity. This finding contrasts with previous results for motion detection and other visual functions in the periphery. The “two visual systems” hypothesis provides a heuristic means of interpreting this apparent discrepancy.     

Representational content and computation in the human visual system

Summary Information-processing systems can be characterized by their ability to transform systematically certain internal representational states (symbols) into one another. The presence of such an information-processing capacity calls for an explanation. How could such an explanation in principle be formulated? How is it possible to specify internal representational states and to ascribe to them certain representational contents? What has to be demonstrated by such explanations is how an information-processing capacity is actually instantiated in a system. In this paper, the outlines of an explanation by instantiation are sketched for a specific human visual capacity. In addition, some fundamental problems facing the development of this explanation will be discussed.     

Visual perception of thick transparent materials

Under typical viewing conditions, human observers readily distinguish between materials such as silk, marmalade, or granite, an achievement of the visual system that is poorly understood. Recognizing transparent materials is especially challenging. Previous work on the perception of transparency has focused on objects composed of flat, infinitely thin filters. In the experiments reported here, we considered thick transparent objects, such as ice cubes, which are irregular in shape and can vary in refractive index. An important part of the visual evidence signaling the presence of such objects is distortions in the perceived shape of other objects in the scene. We propose a new class of visual cues derived from the distortion field induced by thick transparent objects, and we provide experimental evidence that cues arising from the distortion field predict both the successes and the failures of human perception in judging refractive indices.     

The how and why of what went where in apparent motion: modeling solutions to the motion correspondence problem

A model that is capable of maintaining the identities of individuated elements as they move is described. It solves a particular problem of underdetermination, the motion correspondence problem, by simultaneously applying 3 constraints: the nearest neighbor principle, the relative velocity principle, and the element integrity principle. The model generates the same correspondence solutions as does the human visual system for a variety of displays, and many of its properties are consistent with what is known about the physiological mechanisms underlying human motion perception. The model can also be viewed as a proposal of how the identities of attentional tags are maintained by visual cognition, and thus it can be differentiated from a system that serves merely to detect movement.     

Reading through a noisy channel: why there's nothing special about the perception of orthography

The goal of research on how letter identity and order are perceived during reading is often characterized as one of "cracking the orthographic code." Here, we suggest that there is no orthographic code to crack: Words are perceived and represented as sequences of letters, just as in a dictionary. Indeed, words are perceived and represented in exactly the same way as other visual objects. The phenomena that have been taken as evidence for specialized orthographic representations can be explained by assuming that perception involves recovering information that has passed through a noisy channel: the early stages of visual perception. The noisy channel introduces uncertainty into letter identity, letter order, and even whether letters are present or absent. We develop a computational model based on this simple principle and show that it can accurately simulate lexical decision data from the lexicon projects in English, French, and Dutch, along with masked priming data that have been taken as evidence for specialized orthographic representations.     

The visual field paradox: a theoretical account on the reafference principle providing a common frame for the homogeneity and inhomogeneity of visual representation

Observations on the structure of the visual field and its central representation lead to a paradox. A functional dissociation is indicated in oculomotor or attentional control when different response modes are observed as a function of stimulus eccentricity. Alternatively, constancy of brightness throughout the visual field suggests its homogeneity. This paradox can be resolved, if perceptual and motor processes are not conceived of being controlled by separate neuronal mechanisms, but are interconnected within one frame of reference. The reafference principle allows to formulate such a common frame as it integrates afferent and efferent processes. On the basis of this concept, the visual field paradox can be interpreted as not being a paradox at all, but a necessary condition for optimal information processing.     

The independence of dynamic spatial orientation from luminance and refractive error

The effect of refractive error and luminance on circularvection, the illusory sensation of self-motion resulting from rotation of the visual field, was determined. Neither reduction of luminance to levels near absolute scotopic threshold nor induced refractive errors of more than 16 diopters abolished circularvection or influenced any of its latency measures. The results are discussed in terms of the role of the peripheral visual field and the nature of the visual stimulus in ego orientation.     

Bwiti,iboga, trance and healing in Gabon

ABSTRACT

The Bwiti is one out of several religions in Africa and through it, it is believed, that the members can be connected to the world of the ancestors. There is also the ritual of healing in Bwiti. In this ritual, participants are invited to take iboga. They fall into a trance and after this phase, which in principle lasts three days; those who were sick recover the health in many cases. We try to find out in the article, if the change of the state of consciousness like trance can heal. In the end we discover that it is possible. In Bwiti, the change of the paradigm is the most important principle.     

Heuristics and invariants in dynamic event perception: Immunized concepts or nonstatements?

There is ample evidence showing that observers are able to judge dynamic properties of moving objects on the basis of visual kinematics. It is, however, widely disputed as to how to explain this body of data. While direct perceptionists claim that observers have direct access to the underlying dynamics of the event (kinematic specification of dynamics, or KSD, principle), contenders of the perceptual heuristics approach (PH) suggest that observers use the visual equivalent of a heuristic to arrive at their judgments about dynamics. First, the critical assumptions of the KSD principle are discussed in order to motivate the claim that the KSD principle cannot be falsified and is thus immune to empirical criticism. Then the same scrutiny is applied to the PH approach. It is, in its general form at least, afflicted with a similar lack of falsifiability. In comparing the concepts underlying invariants and perceptual heuristics, my conclusion is that a critical experiment aimed at deciding between the two approaches is impossible, and that KSD and PH can be regarded as nonstatements. The findings reported in the event-perception literature must therefore be reevaluated on these grounds.     

Reversing the Attention Effect in Figure-Ground Perception

ABSTRACT— Human visual perception is sometimes ambiguous, switching between different perceptual structures, and shifts of attention sometimes favor one perceptual structure over another. It has been proposed that, in figure-ground segmentation, attention to certain regions tends to cause those regions to be perceived as closer to the observer. Here, we show that this attention effect can be reversed under certain conditions. To account for these phenomena, we propose an alternative principle: The visual system chooses the interpretation that maximizes simplicity of the attended regions.     

Sparse but not 'grandmother-cell' coding in the medial temporal lobe

Although a large number of neuropsychological and imaging studies have demonstrated that the medial temporal lobe (MTL) plays an important role in human memory, there are few data regarding the activity of neurons involved in this process. The MTL receives massive inputs from visual cortical areas, and evidence over the last decade has consistently shown that MTL neurons respond selectively to complex visual stimuli. Here, we focus on how the activity patterns of these cells might reflect the transformation of visual percepts into long-term memories. Given the very sparse and abstract representation of visual information by these neurons, they could in principle be considered as 'grandmother cells'. However, we give several arguments that make such an extreme interpretation unlikely.     

The role of occlusion in the perception of depth, lightness, and opacity

A theory is presented that explains how the visual system infers the lightness, opacity, and depth of surfaces from stereoscopic images. It is shown that the polarity and magnitude of image contrast play distinct roles in surface perception, which can be captured by 2 principles of perceptual inference. First, a contrast depth asymmetry principle articulates how the visual system computes the ordinal depth and lightness relationships from the polarity of local, binocularly matched image contrast. Second, a global transmittance anchoring principle expresses how variations in contrast magnitudes are used to infer the presence of transparent surfaces. It is argued that these principles provide a unified explanation of how the visual system computes the 3-D surface structure of opaque and transparent surfaces.     

Four‐year‐olds incorporate speaker knowledge into pragmatic inferences

Human communication relies on the ability to take into account the speaker's mental state to infer the intended meaning of an utterance in context. For example, a sentence such as ‘Some of the animals are safe to pet’ can be interpreted as giving rise to the inference ‘Some and not all animals are safe to pet’ when uttered by an expert. The same inference, known as a scalar implicature, does not arise when the sentence is spoken by someone with partial knowledge. Adults have been shown to derive scalar implicatures in accordance with the speaker's knowledge state, but in young children this ability is debated. Here, we revisit this question using a simple visual world paradigm. We find that both 4‐ and 5‐year‐olds successfully incorporate speaker knowledge into the derivation of scalar inferences. However, this ability does not generalize immediately to non‐linguistic communicative contexts. These findings have important implications for the development of pragmatic abilities.     

Ophthalmological problems of the premature infant

Preterm infants are more likely than term infants to have significant abnormalities of all parts of the visual system leading to reduced vision. The most common problem is retinopathy of prematurity (ROP). The frequency and severity of this disorder is inversely related to gestational age. Damage ranges from minor to catastrophic. Preterm infants also have higher rates of amblyopia, strabismus, refractive error, and cortical visual impairment. The later problem is largely associated with neonatal brain injury. Years later, these children may develop glaucoma and retinal detachments.