Showing papers on "Foveal published in 1998"

Eye guidance in reading and scene perception

Abstract: Eye guidance in reading, driving and scene perception: introductory notes (G. Underwood, R. Radach). Definition and computation of oculomotor measures in the study of cognitive processes (A. Inhoff, R. Radach). Eye movements and measures of reading time (S. Liversedge et al .). Parafoveal pragmatics (W. Murray). Foveal processing load and landing position effects in reading (S. Liversedge, G. Underwood). The influence of parafoveal words on foveal inspection time: evidence for a processing trade-off (A. Kennedy). Determinants of fixation positions in reading (R. Radach, G. McConkie). Word skipping: implications for theories of eye movement control in reading (M. Brysbaert, F. Vitu). About regressive saccades in reading and their relation to word identification (F. Vitu et al .). Individual differences in reading and eye movement control (J. Everatt et al .). Eye movement control in reading: an overview and a model (K. Rayner et al .). Eye guidance and visual search (J. Findlay, I. Gilchrist). Functional division of the visual field: moving masks and moving windows (P. van Diepen et al .). Prefixational object perception in scenes: objects popping out of schemas (P. De Graef). Visual search of dynamic scenes: event types and the role of experience in viewing driving situations (P. Chapman, G. Underwood). What the driver's eye tells the car's brain (A. Liu). How much do novice drivers see? The effects of demand on visual search strategies in novice and experienced drivers (D. Crundall et al .). The development of eye movement strategies of learner drivers (D. Dishart, M. Land). Film perception: the processing of film cuts (G. d'Ydewalle et al .). Eye movements during scene viewing: an overview (J. Henderson, A. Holingworth).

Eye guidance and visual search

Abstract: Publisher Summary In naturally occurring search situations, eye movements form the most effective way of sampling the visual field. This chapter analyzes the concept of “covert visual attention”. Visual attention can be directed covertly to different locations in the visual field while the eyes themselves are maintained in a fixed position. Redirection of attention in this way gives clear benefits when the speed and accuracy of visual processing at the attended location are measured. The feature integration theory distinguishes between parallel and serial processes in search. Certain search tasks seem easy and effortless, while others tasks seem more arduous and time consuming. Two important assumptions of the theory are “spatial homogeneity of processing”, and “rapid attentional movements”. The visual system is organized so that exquisite detail processing occurs in the central foveal region. Processing ability shows a systematic decline outside this region. The decline is mainly attributable to the properties of the retino cortical mapping function. When more than one stimulus is present in neighboring regions of the peripheral visual field, such stimuli act in a reciprocally interfering manner to produce a further decline in recognition.

The roles of vision and eye movements in the control of activities of daily living.

Abstract: The aim of this study was to determine the pattern of fixations during the performance of a well-learned task in a natural setting (making tea), and to classify the types of monitoring action that the eyes perform.We used a head-mounted eye-movement video camera, which provided a continuous view of the scene ahead, with a dot indicating foveal direction with an accuracy of about 1 deg. A second video camera recorded the subject's activities from across the room. The videos were linked and analysed frame by frame. Foveal direction was always close to the object being manipulated, and very few fixations were irrelevant to the task. The first object-related fixation typically led the first indication of manipulation by 0.56 s, and vision moved to the next object about 0.61 s before manipulation of the previous object was complete. Each object-related act that did not involve a waiting period lasted an average of 3.3 s and involved about 7 fixations. Roughly a third of all fixations on objects could be definitely identified with one of four monitoring functions: locating objects used later in the process, directing the hand or object in the hand to a new location, guiding the approach of one object to another (eg kettle and lid), and checking the state of some variable (eg water level). We conclude that although the actions of tea-making are `automated' and proceed with little conscious involvement, the eyes closely monitor every step of the process. This type of unconscious attention must be a common phenomenon in everyday life. DOI:10.1068/p2935

Relationship between facilitation at threshold and suprathreshold contour integration

Abstract: We reevaluate the facilitation at threshold previously reported between aligned micropatterns and assess the role of such lateral spatial interactions in suprathreshold contour integration tasks. Contrary to previous claims, we show that these interactions are phase dependent. Furthermore, they are clearly evident only for foveal viewing, are not evident for curved alignments (>20°), and do not produce any suprathreshold consequence for contrast perception. Such findings question their usefulness for contour integration of smoothly curved suprathreshold paths.

Eye finding via face detection for a foveated, active vision system

Abstract: Eye finding is the first step toward building a machine that can recognize social cues, like eye contact and gaze direction, in a natural context. In this paper, we present a real-time implementation of an eye finding algorithm for a foveated active vision system. The system uses a motion-based prefilter to identify potential face locations. These locations are analyzed for faces with a template-based algorithm developed by Sinha (1996). Detected faces are tracked in real time, and the active vision system saccades to the face using a learned sensorimotor mapping. Once gaze has been centered on the face, a high-resolution image of the eye can be captured from the foveal camera using a self-calibrated peripheral-ta-foveal mapping.We also present a performance analysis of Sinha's ratio template algorithm on a standard set of static face images. Although this algorithm performs relatively poorly on static images, this result is a poor indicator of real-time performance of the behaving system. We find that our system finds eyes in 94% of a set of behavioral trials. We suggest that alternate means of evaluating behavioral systems are necessary.

The Influence of Parafoveal Words on Foveal Inspection Time: Evidence for a Processing Trade-Off

Abstract: Publisher Summary This chapter describes the influence of parafoveal words on foveal inspection time. It examines the way foveal and parafoveal information combine and interact to determine the timing of eye movements on successive words in text. A crucial question,when fixating a particular word, what information is available from words not yet fixated, is asked and answered. By manipulating the difficulty of the foveal word in different experiments, either by changing word frequency or local syntactic load, it was observed that word frequency or syntactic difficulty manipulations produced similar results. The linguistic properties of the word, or words, being processed, determine from moment to moment the “when and where” of eye movement control. The dynamics of eye movement control in reading are complex and present a major source of variability in measured processing time. The analysis of eye movement measures derived from the unconstrained inspection of text is particularly problematic when trying to interpret experimentally induced variation in fixation duration or saccade extent. Short fixation duration on a word's initial letters reflects, successful prior parafoveal processing. In contrast, short fixation duration on a word's final letters reflects unsuccessful parafoveal processing of the succeeding word.

Indoor monitoring via the collaboration between a peripheral sensor and a foveal sensor

Abstract: In this paper, we describe a novel setup which uses a peripheral sensor and a foveal sensor to perform the indoor monitoring task. The system has the following features: 1) it is constantly aware of the global surrounding, 2) it can dynamically determine its attention to focus on some important events, 3) it achieves real time and reliable performance. In the current implementation, we focus on the events which are triggered by moving persons. Two types of visual agents are used to track moving objects: a peripheral sensing agent that performs global monitoring tasks and a foveal agent that performs focused monitoring tasks. These two heterogeneous sensing agents are coupled in a unique way to work not only asynchronously but also collaboratively via a facilitator. Compared with existing approaches, the proposed scheme provides many advantages in handling the unrestricted movement and various types of occlusions.

Functional Division of the Visual Field: Moving Masks and Moving Windows

Abstract: Publisher Summary The human eyes do not have the same resolution and sensitivity at every position of the retina. Fine details can only be discriminated efficiently by the fovea (the central part of the retina). At higher eccentricities, perceptual acuity decreases rapidly, and only coarse-grained information can be resolved. Consequently, peripheral vision is not particularly suited for object identification or word recognition, as these processes rely on detailed image analyses. Eye movements, or saccades, are required to project image areas onto the fovea. Saccades are not made to random image locations. Most fixations occur on interesting parts of the stimulus, such as words in a text or objects in a scene. Extrafoveal information can be used successfully to guide saccades to informative stimulus locations. By disentangling foveal and peripheral vision the concepts of moving mask and moving window are studied. Coarse peripheral information is preferred to obtain global image characteristics, while object localization gets benefited most from a high resolution peripheral image.

Quantitative analysis of foveal retinal thickness in diabetic retinopathy with the scanning retinal thickness analyzer.

Abstract: PURPOSE This study sought to measure foveal retinal thickness in patients with diabetic retinopathy and to investigate the relationship between foveal thickness and visual acuity, biomicroscopic findings, and angiographic features. METHODS A commercial scanning retinal thickness analyzer was used to measure retinal thickness. A laser slit was projected onto the retina and scanned in 400 milliseconds across the central area of the fundus. The image where the laser slit intersects with the retina was digitally recorded and analyzed. Retinal thickness was measured in 35 patients (35 eyes; patient age, 57 +/- 13 years) with diabetic retinopathy. Patients also were examined by fluorescein angiography and slit-lamp biomicroscopy to detect foveal thickening. RESULTS Linear regression analysis indicated a significant correlation between foveal thickness and visual acuity (adjusted R2 = 0.72, P < 0.001). Foveal thickness was abnormal in 6 (100%) of 6 eyes in which foveal thickening was detected with slit-lamp biomicroscopy. Foveal thickness also was abnormal in 9 (31%) of 29 eyes that appeared normal by biomicroscopic examination. Foveal thickness was 136 +/- 65 microns in 7 eyes without leakage, 175 +/- 35 microns in 13 eyes with questionable leakage, and 291 +/- 120 microns in 7 eyes with definite leakage (P = 0.0075). CONCLUSIONS Retinal thickness analysis is shown to be more sensitive than slit-lamp biomicroscopy for detecting small changes in retinal thickness. Retinal thickness analysis may prove to be a useful, noninvasive modality for the development or regression of macular edema.

Foveal translocation : a comparison of two techniques

Abstract: Subfoveal choroidal neovascular membrane is a leading cause of legal blindness. Photocoagulation has been effective, but photocoagulation of the fovea causes a decrease in vision immediately after treatment. Surgical removal of the choroidal neovascular membrane is effective for choroidal neovascular membrane in some cases, but it restores useful vision for reading (20/40 or better) in a small number of cases of choroidal neovascular membrane not due to presumed ocular histoplasmosis syndrome. A new treatment for subfoveal choroidal neovascular membrane, foveal translocation, is an innovative procedure in which the fovea is translocated onto healthier retinal pigment epithelium. Three techniques have been developed to relocate the retina, 2 of which (retinotomy and scleral shortening) we performed in 5 cases each. Preliminary results in these 10 cases indicate that foveal translocation provides improvement of visual acuity in 40% of eyes and final visual acuities useful for reading (better than 20/40) in ...

Forced peripheral vision driving paradigm: evidence for the hypothesis that car drivers learn to keep in lane with peripheral vision

Abstract: An early well-known hypothesis of Mourant & Rockwell (1970, 1972), which is based on their eye-movement measurements, states that drivers learn to use peripheral vision in lane-keeping while beginners need foveal vision for it. This hypothesis has not been confirmed in real-life experimental settings, however. We recently showed that when forced to do a foveal in-car task, more experienced drivers are better able to keep the car in the lane than novices when the task eccentricity increases from 7 degrees to 23 degrees, thus supporting the hypothesis. This paper reviews two further experiments using the same forced peripheral vision driving paradigm. The first, using a similar representative sample of young male conscripts in similar conditions (lane width of 3m and speed of 30km/h), confirmed the result. The other, using psychology students in conditions closer to normal highway driving (lane width of 3.75m, speed of 60km/h), also included blind-fold driving in order to check the use of kinaesthetic and tactual information in each experience group. The results were in the expected direction but far from significant, presumably due to somewhat different conditions and to the fact that subjects were from highly selected population who were able to develop ad hoc strategies in the task. No experience effect was found in blind-fold performance. The results also showed that the foveal task load does not influence peripheral lane keeping performance, by contrast with the concept that attention within the visual field is a function of foveal load. For the covering abstract see IRRD E102207.

Gaze-contingent video resolution degradation

Abstract: Experimental results are presented evaluating two wavelet- based gaze-contingent video resolution degradation methods under three foveal Region of Interest (ROI) placement strategies. ROI placement is described by the introduction of a novel visualization of viewers' scanpaths, termed Volumes of Interest (VOIs). VOIs represent foveal loci of gaze in 3D space-time. Three ROI placement strategies, ideal, preattentive, and aggregate, are used to determine the location of an unprocessed, dynamic spatial resolution region corresponding to the projected dimension of the fovea. Results indicate imperceptible degradation effects of both ideal and preattentive strategies under a visual tracking paradigm.

Stimulus size scaling and foveal load as determinants of peripheral target detection

Abstract: This paper reports two experiments on the effect of scaling the size of stimuli (using factors derived from consideration of cortical magnification) on the detection of peripheral visual targets. In the first experiment two levels of magnification, fully M-scaled and half M-scaled, were used to scale stimuli that were presented briefly. The performance decrement normally associated with increasing retinal eccentricity did not occur with both levels of magnification. There was an unexpected decline in performance at low eccentricities and possible explanations are discussed. The second experiment investigated the effects of half M-scaling on a peripheral detection task with the addition of foveal cognitive loading as would be found in many practical tasks. Half M-scaling improved performance with and without the presence of foveal loading, and the improvement was greater for the foveal load condition when the target was at the larger eccentricities. These results provide a useful indication of the possibility of reducing the effect of tunnel vision for visual inspection tasks on visual displays or, possibly, control panels through the development of variable resolution projection displays matching the psychophysical properties of the human visual system.

The disappearance of foveal and nonfoveal stimuli : Decomposing the gap effect

Abstract: When a foveal stimulus disappears prior to the appearance of a peripheral target, saccadic reaction times (RTs) are reduced. We compared this gap ef%ect for foveal and nonfoveal stimuli when a highly predictive auditory warning signal was or was not presented. Without a tone, there was a gap effect for both foveal and nonfoveal stimuli; with a tone, there was a gap effect for foveal but not for nonfoveal stimuli. Highly predictive warning tones also modulated the gap effect in a manner that seemed to reflect top-down release of ocular inhibition. We argue that the gap effect therefore consists of three components: (a) warning effects; (b) release of ocular inhibition due to the disappearance of a foveal stimulus; and (c) release of ocular inhibition due to top-down processes. In a gap paradigm, participants are required to maintain gaze on a foveal stimulus until the onset of a peripheral saccade target. On some (overlap) trials, the foveal stimulus remains present; on other (gap) trials, the foveal stimulus is extinguished at some interval prior to the appearance of the target. Saccadic reaction times (RTs) are reduced on gap versus overlap trials (Saslow, 1967). Known as the gap effect, several explanations for this relative facilitation of RTs have been tested and rejected. The longer saccadic RTs on overlap versus gap trials do not result from refractoriness of the saccadic system following fixation-maintaining microsaccades (Kingstone, Fendrich, Wessinger, & Reuter-Lorenz, 1995). The facilitation of saccadic RTs on gap versus overlap trials is not the result of improved visual processing of the target (cf. Reulen, 1984a, 1984b; see Kingstone & Klein, 1993a; ReuterLorenz, Hughes, & Fendrich, 1991). In addition, the gap effect does not reflect the anticipatory execution of preprogrammed saccades on gap trials (cf. Juttner & Wolf, 1992; Kalesnykas & Hallett, 1987; see Kingstone & Klein, 1993a; Reuter-Lorenz et al., 1991). Fischer and colleagues proposed that the facilitation of saccadic RTs following the disappearance of a foveal stimulus may be related to the disengagement of visual attention: When attention is engaged, the saccadic system is inhibited; when attention is disengaged, the saccadic system is released from this inhibition (see Fischer & Weber, 1993 for a review). According to this account, RT facilitation in the typical gap paradigm occurs because the foveal stimulus is also the attended stimulus. It is possible to test this hypothesis by removing attention from the foveal stimulus. If participants are asked to maintain gaze on a foveal stimulus but to attend to a nonfoveal stimulus, the effects of extinguishing the unattended foveal stimulus can be distinguished from the effects of extinguishing the attended nonfoveal stimulus. Unfortunately, early studies that used this strategy to test the attentional disengagement hypothesis were compromised by a failure to assess whether attention was actually allocated to the nonfoveal stimulus (Braun & Breitmeyer,1987; Mayfrank, Mobashery, Kimmig, & Fischer,1986). When Kingstone and Klein (1993a) corrected this methodological weakness, they found that the facilitation of RTs depended on the location of the extinguished stimulus and not on the locus of covert attention. Kingstone and Klein (1993a) presented participants with three stimuli along the vertical meridian. Attention was directed on a trial-by-trial basis to one of the two nonfoveal stimuli on the vertical meridian. This was accomplished via a symbolic cue (Experiments 1 and 3) or via a brightening in the periphery (Experiment 2). On the majority of trials, participants were required to maintain central fixation and to make a speeded manual (button-press) response to report the detection of a target that appeared at one of the two locations on the vertical meridian. To the extent that attention was allocated to the cued location, manual detection RTs were expected to be faster at the cued nonfoveal location than at the uncued nonfoveal location (cf. …

Foveal cysts: a premacular hole condition associated with vitreous traction.

Abstract: Objective To define the clinical findings, cause, and outcome of patients with foveal cysts due to vitreous traction. Methods Follow-up of 18 patients with foveal cysts and no posterior vitreous detachment (PVD). Changes were documented in visual acuity, the appearance of the fovea, or the development of a macular hole or PVD. We studied 8 eyes using the retinal thickness analyzer. Results On follow-up, 9 of 23 eyes did not develop a PVD and still had a foveal cyst; 8 of 23 developed a full-thickness macular hole; 4 of 23 developed a PVD with resolution of the cyst; and 2 eyes underwent vitrectomy for the cyst before a full-thickness hole developed. Analysis with the retinal thickness analyzer showed splitting within the middle retinal layers and in some cases unroofing or absent inner retinal layers in the center of the cyst. Conclusions Foveal cysts are caused by vitreous traction. These eyes may remain stable, develop full-thickness holes, or develop a PVD with resolution of the cystic changes. A foveal cyst seems to be a common finding in patients with foveal traction from a variety of mechanisms.

Foveal automatic target recognition using a multiresolution neural network

Abstract: This paper presents a method for detecting and classifying a target from its foveal (graded resolution) imagery using a multiresolution neural network. Target identification decisions are based on minimizing an energy function. This energy function is evaluated by comparing a candidate blob with a library of target models at several levels of resolution simultaneously available in the current foveal image. For this purpose, a concurrent (top-down-and-bottom-up) matching procedure is implemented via a novel multilayer Hopfield (1985) neural network. The associated energy function supports not only interactions between cells at the same resolution level, but also between sets of nodes at distinct resolution levels. This permits features at different resolution levels to corroborate or refute one another contributing to an efficient evaluation of potential matches. Gaze control, refoveation to more salient regions of the available image space, is implemented as a search for high resolution features which will disambiguate the candidate blob. Tests using real two-dimensional (2-D) objects and their simulated foveal imagery are provided.

Foveal Processing Load and Landing Position Effects in Reading

Abstract: Publisher Summary This chapter describes two eye tracking experiments which investigate whether orthographic information can be extracted from the “parafovea” and used to guide the eye toward infrequent letter strings at the beginning of seven letter target words. It also investigates whether the ease with which the preceding word was processed influenced the degree to which the point of fixation was attracted to an infrequent letter string. In the first experiment, a category word prior to the target word referred to an antecedent noun phrase which was either a typical or an atypical instance of that category is manipulated. In the second experiment, a possessive pronoun to refer to an antecedent noun phrase with a stereotypical gender which was either congruous or incongruous with the gender of the pronoun was tweaked. Reading times during the first pass were not influenced by the two manipulations of foveal load. There were no effects of the frequency of the initial trigram on where within the target word a reader initially fixated. However, the foveal load manipulations caused differences on other eye movement measures indicating the manipulations were not entirely ineffective.

Foveal Dysfunction and Central Visual Field Loss in Glaucoma

Abstract: Objective To determine whether foveal function distal to the ganglion cell layer is an independent predictor of central visual field function in glaucoma. Setting University affiliated hospital and private practice. Participants Twenty-seven eyes (27 patients) with normal-pressure glaucoma, 10 eyes (10 patients) with primary open-angle glaucoma, and 47 eyes of 47 matched normal volunteers. Intervention and Main Outcome Measures Foveal cone electroretinogram (ERG) amplitude, relative optic cup to disc area and their relations to Humphrey full-threshold 30-2 visual field central 4-point mean total deviation (C4MTD) and pattern deviation (C4MPD). Results Foveal cone ERG amplitude was subnormal in 14 (37.8%) of the 37 glaucomatous eyes and lower in the glaucoma group compared with normal eyes (P Conclusion Foveal function distal to the ganglion cell layer and optic disc cupping independently predict central visual field function in glaucoma.

Vision system based on shifted fovea multiresolution retinotopologies

Abstract: In this paper, the authors present a foveal active vision system. It is capable of moving and fixating the fovea to any region of a scene, detecting its most relevant areas to extract certain features of these regions of interest. The system conducts a segmentation of the image, detects the possible existing objects in the scene, obtains hierarchically a set of features for each detected object-centroid, area, bounding box and grey level and extracts the corners of the object contained in the fovea. This system is going to be integrated in an autonomous mobile agent, so it is important to process each object in the optimal resolution level to minimise computational load and time requirements. The most important novelty of the system is the use of reconfigurable shifted fovea retinotopologies, also including a new algorithm capable of obtaining a curvature function by means of local histograms of the contour chain code to reliably calculate the stable corners of the contour of the objects.