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Benjamin W Tatler

Publications and source records attributed to Benjamin W Tatler.

12 recordsLinked to original sources
PubMed2006

Trial by trial effects in the antisaccade task.

The antisaccade task requires participants to inhibit the reflexive tendency to look at a sudden onset target and instead direct their gaze to the opposite hemifield. As such it provides a convenient tool with which to investigate the cognitive and neural systems that support goal-directed behaviour. Recent models of cognitive control suggest that antisaccade performance on a single trial should vary as a function of the outcome (correct antisaccade or erroneous prosaccade) of the previous trial. In addition, repetition priming effects suggest that the spatial location of the target on the previous trial may also influence current trial performance. Thus an analysis of contingency effects in antisaccade performance may provide new insights into the factors that influence the monitoring and modulation of the antisaccade task and other ongoing behaviours. Using a multilevel modelling analysis we explored previous trial effects on current trial performance in a large antisaccade dataset. We found (1) repetition priming effects following correct antisaccades; (2) contrary to models of cognitive control antisaccade error rates were increased on trials following an error, suggesting that failures to adequately maintain the task goal can persist across more than one trial; and (3) current trial latencies varied according to the previous trial outcome (correct antisaccade, slowly corrected error or rapidly corrected error). These results are discussed in terms of current models of antisaccade performance and cognitive control and further demonstrate the utility of multilevel modelling for analysing antisaccade data.

Adult↗
PubMed2006

Global visual scanning abnormalities in schizophrenia and bipolar disorder.

Visual scanning of face images is widely reported to be abnormal in schizophrenia. This impaired processing has been proposed to be partly responsible for patients' disturbance in social interactions. The present study was designed to determine whether abnormal scanning is specific to images with social content or extends to other types of stimuli. Individuals with schizophrenia (n=22), bipolar disorder (n=19) and healthy controls (n=37) were asked to view a series of 28 images with or without socially important content (i.e. faces, landscapes, fractals and noise patterns) while their eye movements were recorded video-oculographically. Temporal and spatial characteristics of scan paths were compared for each patient group and picture type. Independent of image content, patients with schizophrenia exhibited fewer fixations, longer fixation duration, longer saccade duration and peak velocity, and smaller saccade amplitude compared with healthy controls. Patients with schizophrenia and bipolar disorder did not differ significantly from one another on any of the temporal variables recorded. Fixation location distributions of participants with schizophrenia differed significantly from that of healthy controls on all picture types and from patients with bipolar disorder on all but face images. Abnormal scanning in schizophrenia and also bipolar disorder was independent of stimulus type and therefore reflects a global visual scanning impairment not specific to faces. Spatial scanning characteristics but not temporal ones may serve as biomarkers in the functional psychoses.

Adult↗
PubMed2006

High frequency edges (but not contrast) predict where we fixate: A Bayesian system identification analysis.

A Bayesian system identification technique was used to determine which image characteristics predict where people fixate when viewing natural images. More specifically an estimate was derived for the mapping between image characteristics at a given location and the probability that this location was fixated. Using a large database of eye fixations to natural images, we determined the most probable (a posteriori) model of this mapping. From a set of candidate feature maps consisting of edge, contrast and luminance maps (at two different spatial scales), fixation probability was dominated by high spatial frequency edge information. The best model applied compressive non-linearity to the high frequency edge detecting filters (approximately a square root). Both low spatial frequency edges and contrast had weaker, but inhibitory, effects. The contributions of the other maps were so small as to be behaviourally irrelevant. This Bayesian method identifies not only the relevant weighting of the different maps, but how this weighting varies as a function of distance from the point of fixation. It was found that rather than centre surround inhibition, the weightings simply averaged over an area of about 2 degrees.

Bayes Theorem↗
PubMed2006

The long and the short of it: spatial statistics at fixation vary with saccade amplitude and task.

We recorded over 90,000 saccades while observers viewed a diverse collection of natural images and measured low level visual features at fixation. The features that discriminated between where observers fixated and where they did not varied considerably with task, and the length of the preceding saccade. Short saccades (<8 degrees) are image feature dependent, long are less so. For free viewing, short saccades target high frequency information, long saccades are scale-invariant. When searching for luminance targets, saccades of all lengths are scale-invariant. We argue that models of saccade behaviour must account not only for task but also for saccade length and that long and short saccades are targeted differently.

Adolescent↗
PubMed2005

Visual correlates of fixation selection: effects of scale and time.

What distinguishes the locations that we fixate from those that we do not? To answer this question we recorded eye movements while observers viewed natural scenes, and recorded image characteristics centred at the locations that observers fixated. To investigate potential differences in the visual characteristics of fixated versus non-fixated locations, these images were transformed to make intensity, contrast, colour, and edge content explicit. Signal detection and information theoretic techniques were then used to compare fixated regions to those that were not. The presence of contrast and edge information was more strongly discriminatory than luminance or chromaticity. Fixated locations tended to be more distinctive in the high spatial frequencies. Extremes of low frequency luminance information were avoided. With prolonged viewing, consistency in fixation locations between observers decreased. In contrast to [Parkhurst, D. J., Law, K., & Niebur, E. (2002). Modeling the role of salience in the allocation of overt visual attention. Vision Research, 42 (1), 107-123] we found no change in the involvement of image features over time. We attribute this difference in our results to a systematic bias in their metric. We propose that saccade target selection involves an unchanging intermediate level representation of the scene but that the high-level interpretation of this representation changes over time.

Attention↗
PubMed2005

Visual memory for objects in natural scenes: from fixations to object files.

Object descriptions are extracted and retained across saccades when observers view natural scenes. We investigated whether particular object properties are encoded and the stability of the resulting memories. We tested immediate recall of multiple types of information from real-world scenes and from computer-presented images of the same scenes. The relationship between fixations and properties of object memory was investigated. Position information was encoded and accumulated from multiple fixations. In contrast, identity and colour were encoded but did not require direct fixation and did not accumulate. In the current experiments, participants were unable to recall any information about shape or relative distances between objects. In addition, where information was encoded we found differential patterns of stability. Data from viewing real scenes and images were highly consistent, with stronger effects in the real-world conditions. Our findings imply that object files are not dependent upon the encoding of any particular object property and so are robust to dynamic visual environments.

Adult↗
PubMed2003

On nystagmus, saccades, and fixations.

Investigations of the ways in which the eyes move came to prominence in the 19th century, but techniques for measuring them more precisely emerged in the 20th century. When scanning a scene or text the eyes engage in periods of relative stability (fixations) interspersed with ballistic rotations (saccades). The saccade-and-fixate strategy, associated with voluntary eye movements, was first uncovered in the context of involuntary eye movements following body rotation. This pattern of eye movements is now referred to as nystagmus, and involves periods of slow eye movements, during which objects are visible, and rapid returns, when they are not; it is based on a vestibular reflex which attempts to achieve image stabilisation. Post-rotational nystagmus was reported in the late 18th century (by Wells), with afterimages used as a means of retinal stabilisation to distinguish between movement of the eyes and of the environment. Nystagmus was linked to vestibular stimulation in the 19th century, and Mach, Breuer, and Crum Brown all described its fast and slow phases. Wells and Breuer proposed that there was no visual awareness during the ballistic phase (saccadic suppression). The saccade-and-fixate strategy highlighted by studies of nystagmus was shown to apply to tasks like reading by Dodge, who used more sophisticated photographic techniques to examine oculomotor kinematics. The relationship between eye movements and perception, following earlier intuitions by Wells and Breuer, was explored by Dodge, and has been of fundamental importance in the direction of vision research over the last century.

Eye Movements↗
PubMed2003

The time course of abstract visual representation.

Studies in change blindness re-enforce the suggestion that veridical, pictorial representations that survive multiple relocations of gaze are unlikely to be generated in the visual system. However, more abstract information may well be extracted and represented by the visual system. In this paper we study the types of information that are retained and the time courses over which these representations are constructed when participants view complex natural scenes. We find that such information is retained and that the resultant abstract representations encode a range of information. Different types of information are extracted and represented over different time courses. After several seconds of viewing natural scenes, our visual system is able to construct a complex information-rich representation.

Adolescent↗
PubMed2003

Dodge-ing the issue: Dodge, Javal, Hering, and the measurement of saccades in eye-movement research.

Dodge, in 1916, suggested that the French term 'saccade' should be used for describing the rapid movements of the eyes that occur while reading. Previously he had referred to these as type I movements. Javal had used the term 'saccade' in 1879, when describing experiments conducted in his laboratory by Lamare. Accordingly, Javal has been rightly credited with assigning the term to rapid eye movements. In English these rapid rotations had been called jerks, and they had been observed and measured before Lamare's studies of reading. Rapid sweeps of the eyes occur as one phase of nystagmus; they were observed by Wells in 1792 who used an afterimage technique, and they were illustrated by Crum Brown in 1878. Afterimages were used in nineteenth-century research on eye movements and eye position; they were also employed by Hering in 1879, to ascertain how the eyes moved during reading. In the previous year, Javal had employed afterimages in his investigations of reading, but this was to demonstrate that the eyes moved horizontally rather than vertically. Hering's and Lamare's auditory method established the discontinuous nature of eye movements during reading, and the photographic methods introduced by Dodge and others in the early twentieth century enabled their characteristics to be determined with greater accuracy.

Biomedical Research↗
PubMed2002

What information survives saccades in the real world?

Recent change detection research demonstrates impressively that we do not retain and fuse the pictorial content of successive fixations. This raises two distinct issues: (1) when and how is point-by-point information lost or replaced? and (2) might more abstract information be extracted and retained from fixations? In this chapter I explore both of these issues. I consider the evidence for a very short-term richly detailed visual representation of the current target of fixation that survives the saccade but is overwritten by the content of each new fixation shortly after it begins. The possibility of abstract representations of the visual surroundings is then discussed. Under conditions of competitive, parallel processing, as are present in real life situations, multiple types of information are extracted and retained from complex natural scenes. Time courses for extraction vary between different types of information. The inclusion of eye movement data reveals a crucial role for fixations in information extraction. The data suggest that information assimilation into the representations tested here is dominated by the fovea and is integrated and accumulated from multiple foveations. From these studies we are able to construct a rudimentary framework, in which representational faithfulness and richness depend upon fixation history of that part of the visual scene, thus producing an efficient and potentially task-specific representation.

Fixation, Ocular↗