Claus Bundesen

Abstract A series of experiments on skilled readers of Chinese demonstrated selective attention to different orthographic components within compound, single-character words, as a function of different reading tasks (pronunciation vs. meaning). Chinese orthography ...

Phasic alertness refers to a short-lived change in the preparatory state of the cognitive system following an alerting signal. In the present study, we examined the effect of phasic auditory alerting on distinct perceptual processes, unconfounded by motor components. We combined an alerting/no-alerting design with a pure accuracy-based single-letter recognition task. Computational modeling based on Bundesen's Theory of Visual Attention was used to examine the effect of phasic alertness on visual processing speed and threshold of conscious perception. Results show that phasic auditory alertness affects visual perception by increasing the visual processing speed and lowering the threshold of conscious perception (Experiment 1). By manipulating the intensity of the alerting cue, we further observed a positive relationship between alerting intensity and processing speed, which was not seen for the threshold of conscious perception (Experiment 2). This was replicated in a third exper...

Publikationsansicht. 31491192. Studier af visuel informationsbehandling : sammenfattende redegørelse / (1986). Bundesen, Claus. Abstract. Tevens proefschrift København.. Met lit.opg.: p. 42-51. Details der Publikation. Download, http://worldcat.org/oclc/64362745. ...

A fundamental question concerning the way the visual world is represented in our brain is how a cortical cell responds when its classical receptive field contains a plurality of stimuli. Two opposing models have been proposed. In the response-averaging model, the neuron responds with a weighted average of all individual stimuli. By contrast, in the probability-mixing model, the cell responds to a plurality of stimuli as if only one of the stimuli were present. Here we apply the probability-mixing and the response-averaging model to leaky integrate-and-fire neurons, to describe neuronal behavior based on observed spike trains. We first estimate the parameters of either model using numerical methods, and then test which model is most likely to have generated the observed data. Results show that the parameters can be successfully estimated and the two models are distinguishable using model selection.

The theory of visual attention introduced by Bundesen (1990) is reviewed. The authors first describe TVA as a formal computational theory of visual attention and summarize applications of TVA to psychological studies of performance (reaction times and error rates) in healthy human subjects. They then explain their neurophysiological interpretation of TVA, NTVA, and exemplify how NTVA accounts for findings from single-cell studies in primates. Finally the authors review how TVA has been applied to study attentional functions in neuropsychological, pharmacological, and genetic research.

We report on a patient who complained of reduced awareness in the left visual field, but showed no visual neglect or extinction in clinical testing. By MR scanning, the brain damage was localized to the right basal ganglia, also involving structures in right frontal cortex. Using psychophysical testing and mathematical modeling based on Bundesen's theory of visual attention [TVA; Psychol. Rev. 97 (1990) 523], the patient's subjective experience of attentional disturbance was confirmed, and the deficit was specified into several components. At very short exposure durations, two effects were shown. The detection threshold was elevated, particularly in the left visual field, and stimuli in this side were given less attentional weight. In addition, the capacity of visual short-term memory (VSTM) was markedly reduced in both visual fields. The robustness of the test results was evaluated by bootstrap analysis. The study demonstrates the sensitivity and specificity gained by combining psychophysical testing with TVA modeling in the analysis of visual attention disorders. Extending the results of a pioneer study of parietal neglect patients by Duncan et al. [J. Exp. Psychol.: Gen. 128 (1999) 450], this study demonstrates the strength of the method in a single case, with a lesion outside parietal cortex, and only minor clinical symptoms.

A physiologically based nonhomogeneous Poisson counter model of visual identification is presented. The model was developed in the framework of a Theory of Visual Attention (Bundesen, 1990; Kyllingsbæk, Markussen, & Bundesen, 2012) and meant for modeling visual identification of objects that are mutually confusable and hard to see. The model assumes that the visual system's initial sensory response consists in tentative visual categorizations, which are accumulated by leaky integration of both transient and sustained components comparable with those found in spike density patterns of early sensory neurons. The sensory response (tentative categorizations) feeds independent Poisson counters, each of which accumulates tentative object categorizations of a particular type to guide overt identification performance. We tested the model's ability to predict the effect of stimulus duration on observed distributions of responses in a nonspeeded (pure accuracy) identification task wit...

ABSTRACT The limitations of the visual short-term memory (VSTM) system have become an increasingly popular field of study. One line of inquiry has focused on the way attention selects objects for encoding into VSTM. Using the framework of the Theory of Visual Attention (TVA; Bundesen, 1990, Psychological Review,97, 523-547) different components of attention were measured while arousal was systematically varied by manipulating temporal expectancies of the observer. The results showed increments in both overall speed of encoding into VSTM and efficiency of visual selection as the level of arousal was increased, whereas VSTM capacity showed some decrease with increasing arousal. Furthermore, attentional weights seemed to be modulated such that, as arousal increased, the attentional focus narrowed around fewer, highly relevant objects. Arousal seems to interact with attention in two different ways: Through a scaling mechanism modulating the decision bias of the observer and also through an accentuation-suppression mechanism that modulates the degree of subjective relevance of objects, contracting attention around fewer, highly relevant objects while suppressing less relevant objects. These mechanisms may afford an evolutionary advantage for an observer, ensuring that the most relevant objects are selected and encoded faster under high arousal, and making later processing more focused as the capacity of VSTM is decreased.

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder which frequently persists into adulthood. The primary goal of the current study was to (a) investigate attentional functions of stimulant medication-naïve adults with ADHD, and (b) investigate the effects of 6 weeks of methylphenidate treatment on these functions. The study was a prospective, non-randomized, non-blinded, 6-week follow-up design with 42 stimulant medication-naïve adult patients with ADHD, and 42 age and parental education-matched healthy controls. Assessments included measures of visual attention, based on Bundesen's Theory of Visual Attention (TVA), which yields five precise measures of aspects of visual attention; general psychopathology; ADHD symptoms; dyslexia screening; and estimates of IQ. At baseline, significant differences were found between patients and controls on three attentional parameters: visual short-term memory capacity, threshold of conscious perception, and to a l...

A fundamental question concerning representation of the visual world in our brain is how a cortical cell responds when presented with more than a single stimulus. We find supportive evidence that most cells presented with a pair of stimuli respond predominantly to one stimulus at a time, rather than a weighted average response. Traditionally, the firing rate is assumed to be a weighted average of the firing rates to the individual stimuli (response-averaging model) (Bundesen et al., 2005). Here, we also evaluate a probability-mixing model (Bundesen et al., 2005), where neurons temporally multiplex the responses to the individual stimuli. This provides a mechanism by which the representational identity of multiple stimuli in complex visual scenes can be maintained despite the large receptive fields in higher extrastriate visual cortex in primates. We compare the two models through analysis of data from single cells in the middle temporal visual area (MT) of rhesus monkeys when presen...

The effect of letter confusability on reading has received increasing attention over the last decade. Confusability scores for individual letters, derived from older psychophysical studies, have been used to calculate summed confusability scores for whole words, and effects of this variable on normal and alexic reading have been reported. On this basis, letter confusability is now increasingly controlled for in stimulus selection. In this commentary, we try to clarify what letter confusability scores represent and discuss several problems with the way this variable has been treated in neuropsychological research. We conclude that it is premature to control for this variable when selecting stimuli in studies of reading and alexia. Although letter confusability may play a role in (impaired) reading, it remains to be determined how this measure should be calculated, and what effect it may have on word and letter identification.

Current behavior is influenced by events in the recent past. In visual attention, this is expressed in many variations of priming effects. Here, we investigate color priming in a brief exposure digit-recognition task. Observers performed a masked odd-one-out singleton recognition task where the target-color either repeated or changed between subsequent trials. Performance was measured by recognition accuracy over exposure durations. The purpose of the study was to replicate earlier findings of perceptual priming in brief displays and to model those results based on a Theory of Visual Attention (TVA; Bundesen, 1990). We tested 4 different definitions of a generic TVA-model and assessed their explanatory power. Our hypothesis was that priming effects could be explained by selective mechanisms, and that target-color repetitions would only affect the selectivity parameter (α) of our models. Repeating target colors enhanced performance for all 12 observers. As predicted, this was only true under conditions that required selection of a target among distractors, but not when a target was presented alone. Model fits by TVA were obtained with a trial-by-trial maximum likelihood estimation procedure that estimated 4-15 free parameters, depending on the particular model. We draw two main conclusions. Color priming can be modeled simply as a change in selectivity between conditions of repetition or swap of target color. Depending on the desired resolution of analysis; priming can accurately be modeled by a simple four parameter model, where VSTM capacity and spatial biases of attention are ignored, or more fine-grained by a 10 parameter model that takes these aspects into account.

In the partial-report task, subjects are asked to report only a portion of the items presented. Selective attention chooses which objects to represent in short-term memory (STM) on the basis of their relevance. Because STM is limited in capacity, one must sometimes choose which objects are removed from memory in light of new relevant information. We tested the hypothesis that the choices among newly presented information and old information in STM involve the same process-that both are acts of selective attention. We tested this hypothesis using a two-display partial-report procedure. In this procedure, subjects had to select and retain relevant letters (targets) from two sequentially presented displays. If selection in perception and retention in STM are the same process, then irrelevant letters (distractors) in the second display, which demanded attention because of their similarity to the targets, should have decreased target report from the first display. This effect was not obt...

In visual search, inefficient performance of human observers is typically characterized by a steady increase in reaction time with the number of array elements—the so-called set-size effect. In general, set-size effects are taken to indicate that processing of the array elements depends on limited-capacity resources, that is, it involves attention. Contrasting theories have been proposed to account for this attentional involvement, however. While some theories have attributed set-size effects to the intervention of serial attention mechanisms, others have explained set-size effects in terms of parallel, competitive architectures. Conclusive evidence in favor of one or the other notion is still lacking. Especially in view of the wide use of visual search paradigms to explore the functional neuroanatomy of attentional mechanisms in the primate brain, it becomes essential that the nature of the attentional involvement in these paradigms be clearly defined at the behavioral level. Here we report a series of experiments showing that highly inefficient search indeed recruits serial attention deployment to the individual array elements. In addition, we describe a number of behavioral signatures of serial attention in visual search that can be used in future investigations to attest a similar involvement of serial attention in other search paradigms. We claim that only after having recognized these signatures can one be confident that truly serial mechanisms are engaged in a given visual search task, thus making it amenable for exploring the functional neuro-anatomy underlying its performance.

In the present study, we investigated effects of phasic alerting on visual attention in a partial report task, in which half of the displays were preceded by an auditory warning cue. Based on the computational Theory of Visual Attention (TVA), we estimated parameters of spatial and non-spatial aspects of visual attention and measured event-related lateralizations (ERLs) over visual processing areas. We found that the TVA parameter sensory effectiveness a, which is thought to reflect visual processing capacity, significantly increased with phasic alerting. By contrast, the distribution of visual processing resources according to task relevance and spatial position, as quantified in parameters top-down control α and spatial bias windex, was not modulated by phasic alerting. On the electrophysiological level, the latencies of ERLs in response to the task displays were reduced following the warning cue. These results suggest that phasic alerting facilitates visual processing in a genera...

... Talk Bachmann Alan Baddeley Graham Beaumont Paul Bertelson Bruce Bridgeman Vicki Bruce Claus Bundesen Fergus Craik Michel Denis Dietrich Dom& ... Lawrence Erlbaum Associates Ltd., 27 Palmeira Mansions, Church Road, Hove, East Sussex BN3 2FA. ...

... Talk Bachmann Alan Baddeley Graham Beaumont Paul Bertelson Bruce Bridgeman Vicki Bruce Claus Bundesen Fergus Craik Michel Denis Dietrich Dom& ... Lawrence Erlbaum Associates Ltd., 27 Palmeira Mansions, Church Road, Hove, East Sussex BN3 2FA. ...

1. Acta Psychol (Amst). 2010 Oct;135(2):106-8; discussion 133-9. Epub 2010 Jun 2. Is initial visual selection completely stimulus-driven? Nordfang M, Bundesen C. Department of Psychology, University of Copenhagen, Copenhagen, Denmark. maria.nordfang@psy.ku.dk. ...

Nissen (1985) compared selection by location with selection by color or shape in partial-report experiments. Her analysis of response contingencies when a target was defined in terms of one attribute (location, color, or shape), and when the task was to report the two remaining attributes, suggested a special role for selection by location: It appeared that cross-referencing between color and

... ofPsychology, Har-vard Univ., 33 Kirkland St., Cambridge, MA 02138) "Apparent duration and spatial structure" by J. Hughes, JR Lishman, & DM ... 3LE, UK) "Suppression of optokinesis by a stabilized target: Effects of instruction and stimulus frequency" by J. Pola, HJ Wyatt, & M ...