Visual Search Time Research Articles

Assessing Design Features of Virtual Keyboards for Text Entry

The present research examined design of a virtual keyboard for text entry with a rotary controller, emphasizing users who differ in age and system experience. Existing research has minimally addressed usage frequency, age, and the effects of display shape and letter arrangement on movement and visual search components of text entry tasks. The present research was conducted to close these gaps. Two experiments were completed to examine younger (18-28 years) and older (60-75 years) adults' movement and visual search capabilities using four keyboard shapes and three keyboard arrangements. In a third experiment examining combined effects on shape design, 32 younger (18-28 years) and 32 older (60-75 years) adults entered words on the two best shapes from the first experiments. For the movement task, movement time was lowest for shapes with higher shape-controller compatibility. For the visual search task, search time and accuracy were best on the alphabetic arrangement. In the combined task, shape did not significantly influence performance at different levels of practice. Transfers, however, suggested that the shape with salient visual features elicited a text entry strategy for older adults that may promote more consistent performance under occasional usage. The studies together demonstrate that keyboard shape is important for efficient performance. Shape-controller compatibility facilitated performance in both age groups. Salient features facilitate performance, especially for older adults. In nearly all cases alphabetic arrangement yielded the best performance. Recommendations are provided for virtual keyboard design for different usage frequencies, contexts, and users.

Lobe size curves for several targets and their effect on visual search time

A series of experiments was conducted to obtain horizontal axis lobe size data for each of the six target characters in a complex background of 10 other characters, then two of these targets on the vertical axis, and finally the same two at five different heights on the horizontal axis. Secondly, a series of search time (ST) experiments was run for the same combinations but with larger background areas. The lobe size experiments gave linear regression lines for the probability of detecting a target versus its distance from the fixation point. But there was not much difference due to shape or size of the targets. From the ST data, a linear relationship was found between log ST and log (target height). The ST data were also used to calculate effective lobe sizes which were used with the hard shells of the initial lobe size data to find the effective diameter and effective probability of detecting a target. From these, the log mean ST was found to have a linear relationship with the log of the effective probability. Effective diameter of the lobe was a better estimate to use for estimating ST than data obtained from the hard shell approach, and the results suggest that factors other than lobe size, such as peripheral vision, information processing, and elements of pattern recognition had a major effect on the ST results. Relevance to industry This research can help employers in industry to find which inspectors will be better suited to particular jobs, and also enable them to estimate better the time needed to perform such jobs at a good level of performance.

Unconscious associative memory affects visual processing before 100 ms

Searching for an object in a cluttered environment takes advantage of different cues, explicit attentional cues, such as arrows, and visual cues, such as saliency, but also memory. Behavioral studies manipulating the spatial relationships between context and target in visual search suggest that the memory of context-target associations could be retrieved quickly and act at an early perceptual stage. On the other hand, neural responses are usually influenced by memory at a later, postperceptual stage. At which level of neural processing does the memory of context-target associations influence scene analysis? In our experiment, human subjects learned arbitrary associations between given spatial layouts of distractors and target positions while performing a classical visual search task. Behaviorally, context-target associations speed visual search times, although subjects remain fully unaware of these associations. Magneto-encephalographic responses to visual displays containing or not containing relevant contextual information differ before 100 ms, much earlier than any known effect of recent experience. This effect occurs bilaterally at occipital sensors only, suggesting that context affects activity in the underlying early sensory cortices. Importantly, subjects do not show any sign of explicit knowledge about context-target associations: The earliness of the influence of contextual knowledge may be a hallmark of unconscious memory.

Shape characteristics of useful field of view and visual search time

LA FORME ET LES CARACTÉRISTIQUES DU CHAMP VISUEL UTILE IMPLIQUÉ DANS LA RECHERCHE VISUELLE Le champ visuel utile (CVU) correspond à la partie du champ visuel dans laquelle il est possible d’extraire un maximum d’informations. Ce CVU ne recouvre pas l’ensemble du champ visuel. Déterminer la forme et les caractéristiques du CVU impliqué dans l’activité de recherche visuelle revêt alors une importance certaine pour les applications dans le domaine industriel, voire dans la vie quotidienne. Généralement, les théories explicatives de la recherche visuelle postulent que le champ visuel a une forme circulaire ou elliptique alors que nombre de travaux insistent sur le caractère irrégulier du CVU. La présente étude vise à étudier de façon détaillée, les caractéristiques de forme du CVU, son degré de sphéricité, la régularité des ses frontières, son étirement longitudinal et sa régularité globale, et à identifier lesquels de ces index de forme sont le plus impliqués dans le processus de recherche visuelle. Pour cela deux expériences ont été menées. La première, impliquant 101 sujets, porte sur la forme du CVU, en découpant le champ visuel en 24 zones méridiennes et en déterminant dans chaque zone, la partie active en recherche visuelle. Comme attendu, la majeure partie des CVU sont irréguliers, sans forme circulaire ou ovoïde évidente. Les résultats montrent également que les CVU sont plutôt étirés sur un axe horizontal, avec des frontières plutôt régulières et des niveaux de symétrie et de régularité médians. Les corrélations entre temps de recherche visuelle et les cinq index font ressortir l’importance de la forme sphérique, de la régularité des frontières et de la forme. La deuxième expérience porte plus particulièrement sur l’intérêt de ces indices de forme pour prédire la performance en recherche visuelle. Les indices de forme du CVU permettent effectivement de renforcer les modèles de régression explicatifs de la performance visuelle. Cette étude démontre finalement l’intérêt d’identifier et d’évaluer les indices, en particulier avec le système visuel de mesure du CVU (VILOMS), développé par les auteurs. Le système permet de prendre en compte une grande variété d’indices pour élaborer des modèles de recherche visuelle et sélectionner et former les professionnels engagés dans des tâches d’inspection.

A scale invariant measure of clutter

We propose a measure of clutter for real images that can be used to predict search times. This measure uses an efficient segmentation algorithm (P. Felzenszwalb & D. Huttenlocher, 2004) to count the number of regions in an image. This number is not uniquely defined, however, because it varies with the scale of segmentation. The relationship between the number of regions and the scale of segmentation follows a power law, and the exponent of the power law is similar across images. We fit power law functions to the multiple scale segmentations of 160 images. The power law exponent was set to the average value for the set of images, and the constant of proportionality was used as a measure of image clutter. The same 160 images were also used as stimuli in a visual search experiment. This scale-invariant measure of clutter accounted for about 40% of the variance in the visual search times.

Visual lobe shape and search performance for targets of different difficulty

In quantitative models of visual search it has usually been assumed that visual lobe area shape was sufficiently regular to be approximated by a circle or ellipse. However, the irregularities in visual lobe shapes that have been found in studies involving extensive lobe mapping have suggested that lobe shape may have important implications for visual search performance and for the accuracy of mathematical models used for performance prediction. However, no systematic research on the relationship between the shape aspect of visual lobes and search performance seems to have been carried out and no comparisons of visual lobe shape characteristics under the effect of target difficulty have been reported. The current study was conducted to achieve two major objectives in two experiments. Experiment 1 used two different targets (letter ‘O’ and letter ‘Y’) to map the visual lobes of subjects in order to provide a systematic and quantitative comparison of lobe shape characteristics and experiment 2 was to investigate the correlation of visual lobe shape characteristics with visual search time under the effect of target difficulty. The visual lobes of 28 subjects were mapped on 24 imaginary and regularly spaced meridians originating from the centre of the visual field to resemble the full field mapping situation. Five categories of shape indices, viz. roundness, boundary smoothness, symmetry, elongation and shape regularity were investigated. The results of this study demonstrated that the visual lobe shapes of subjects elongate horizontally with medium level of roundness, high levels of boundary smoothness, symmetry and regularity for an easy target (O) against a homogeneous background of ‘X’s. When a difficult target (Y) was used, the visual lobes of the subjects were still elongated horizontally but to a smaller extent and with a low level of roundness, medium level of boundary smoothness and regularity and a similar high level of symmetry to the easy target. Moreover, significant correlations between shape indices and visual search time were found, suggesting mathematical models for predicting search time should not merely rely on area but also should consider visual lobe shape indices. Finally, a universal mathematical model containing several visual lobe shape indices was developed, which was applicable in the prediction of visual search time for a range of similar search tasks.

The use of visual search to assess attention

Background: Under some conditions, the time required for a visual search increases with the number of elements to be searched. It has been suggested that the overall search time reflects the duration that attention is devoted to each element multiplied by the number of elements. On this basis, it has been proposed that visual search time can be used as a measure of attention capability in dyslexic readers. However, there is evidence to suggest that the search time reflects task difficulty rather than attentional factors. Many dyslexic readers suffer from various sensory deficits. These deficits would effectively increase task difficulty for these readers. Here we use computer simulations to investigate the potential effects of sensory deficits on visual search.Method: Visual search was modelled on a computer within the framework of signal detection theory as a matter of detecting a noisy signal from a series of noisy distractors. Sensory deficits were modelled as decreased discriminability.Results: Consistent with previous observations, we find that discriminability, which decreases with the number of distractors, may have a substantial effect on the search time. With regard to the effects of sensory deficits, we find that under low discriminability conditions, small sensory deficits may cause pronounced increases in search time.Conclusion: The finding that small sensory deficits may cause pronounced increases in search time makes it specifically problematic to use visual search to test attention in individuals who suffer from sensory deficits. This applies particularly to dyslexic individuals, many of whom have been shown to suffer from visual deficiencies.

Examining the Viability of the Neisser Search Model in the Flight Domain and the Benefits of Highlighting in Visual Search

We conducted four experiments to examine the visual search capability of pilots and examine how search times could be reduced, invoking the framework of Neisser's serial self terminating (SST) search model. In Experiment 1 which manipulated target presence and set size, our results show increases in response time as array size increases: an effect predicted by the SST model. In Experiment 2, we manipulated the background against which the visual search had to be performed. We found that the detrimental effects of array size on visual search time are maximal when the search is performed against maps, which have large quantities of terrain information. In Experiment 3, we sought to assess the degree to which high and low-lighting could be used to reduce the search times of pilots. We observed that although both high and lowlighting reduced the search times of pilots, the observed reductions were not predicted by the SST model. The advantage of highlighting elements of the target was shown in Experiment 4.

Effects of retinal image degradation on pre‐attentive visual search (PAVS) efficiency for flicker, movement and orientation stimuli

Previous research has shown that several clinical conditions cause increased pre-attentive visual search (PAVS) times, implying reduced parallel search capabilities in glaucoma and DLB dementia. The purpose of the research reported here was to examine for the first time the resistance of PAVS to dioptric blur using targets differing from the background in terms of flicker, vertical displacement, and orientation. Resistance would enhance the applicability of PAVS as a screening method for glaucoma and other clinical conditions affecting performance of a substantial area of the retina. Computer generated flicker, orientation and vertical displacement targets were used to assess PAVS efficiency. The subject's task was to locate a small single target subtending 0.92 degrees as quickly as possible (embedded in a field of 119 distractors) on either the left- or right-hand side of a computer monitor. Average PAVS response times were calculated for 40 presentations of each target type presented randomly in any one of 120 positions within +/-15 degrees of fixation. Subjects performed the test using their distance spectacles (unless emmetropic), then three tests using positive lenses simulating myopia of up to -3 D, and finally using optimum correction again. ANOVA revealed that blur of up to 3 D had no statistically significant effect on response times to the flicker target. Blur of over 2.0 D however resulted in increased response times for the displacement target, but only for eyes which were not cyclopleged. The orientation target became significantly more difficult to locate, response times becoming progressively slower with increasing levels of blur (p < 0.05%). The present flicker and displacement targets are relatively resistant to the effects of reduced acuity, while the orientation target is only suitable for testing subjects with good visual acuity.

Visual search and eye movements in patients with chronic solvent-induced toxic encephalopathy

Various aspects of visual perception have been found to be impaired in patients with occupational chronic solvent-induced toxic encephalopathy (CSE). The purpose of the study was to characterise the changes in eye movements and visual search performance in CSE patients. We measured eye movements of 13 CSE patients and 22 healthy controls during dynamic visual search task by using a fast video eye tracker. The task was to search for and identify a target letter among numerals presented in a rectangular stimulus matrix (3 × 3–10 × 10 items). Threshold search time, i.e. the duration of stimulus presentation required for identifying the target with a given probability was determined by using a psychophysical staircase method. The visual search times of the CSE patients were clearly longer, and they needed considerably more eye fixations than healthy controls to find the target. Thus, their reduced performance in this task was mainly related to the reduction in the number of items which could be processed during a single eye fixation ( perceptual span). This reduction probably reflects a limited capacity of visual attention, since visual acuity, contrast sensitivity, and the oculomotor saccade velocity were found to be normal. The results suggest that motor slowness or low-level visual factors do not explain the poor performance of CSE patients in visual search tasks. The results are also discussed with respect to the effects of education, and compared to the performance in the widely used neuropsychological Trail Making Test, which uses similar stimuli and requires visual search.

A simulated study on the effects of information volume on traffic signs, viewing strategies and sign familiarity upon driver's visual search performance

A two-stage simulation experiment was conducted to investigate the effect of information volume on traffic regulatory/road direction signs, drivers’ viewing strategies and sign familiarity on performance in visual search. In Stage I experiment, the amount of information on a total of 187 traffic regulatory and 1272 road direction signs was calculated and divided into five information levels using cluster analysis. In Stage II experiment, 24 subjects participated in a 2 (familiarity)×5 (information volume level)×2 (viewing strategy) mixed factorial experiment. Each subject was required to perform a visual search task and a question-and-answer (Q&A) task. Visual search time and number of correct responses collected serve as the objective dependent variables. Subjective workload related to time stress and visual effort was gathered through a modified three-point rating. Results show that information volume on traffic signs had significant impact on drivers’ visual search performance. Generally, the greater the amount of information, the slower the drivers in visual search are. However, while drivers had the highest accuracy rate in remembering purely pictorial traffic signs, these signs within the smallest information volume level required a relatively longer search time. Different viewing strategies also led to different performances. The back-and-forth strategy yielded better search performance than the fixed strategy. Subjective workload evaluation indicates that drivers with less sign familiarity will be under greater time/visual pressures. Guidelines for designing for traffic signs or in-vehicle signing systems are provided. Relevance to industry This study calculated the amount of information on traffic signs and compared the effects of different information volume on drivers’ visual search performance. The results can provide guidelines for traffic sign designers to help decide on the presentation format for in-vehicle signing information systems.

Dynamic visual fields of one-eyed observers

The horizontal binocular visual field can extend to more than 200 degrees, while a monocular field is limited to 160 degrees. Additionally, the nose and other facial structures may block the monocular field further during certain eye movements. The purpose of this study was to compare the monocular against the binocular visual field and determine if head and eye movements can functionally overcome any measured deficit. In Experiment 1, visual fields were measured monocularly with a bowl perimeter using 5 fixation positions. Binocular visual fields were calculated by combining the monocular visual field with its mirror image. In Experiment 2, subjects were allowed to make head, eye, and body movements to search for flashing lights 360 degrees around them, spaced every 45 degrees. The numbers of lights identified were compared for the subjects performing monocularly versus binocularly. The size of the overall monocular visual field was found to vary between 48% and 76% of the binocular visual field, depending on eye position. For the flashing light experiment, head and eye movements could not overcome the entire visual-field deficit with monocular viewing. Monocular performance remained 11.4% less than binocular performance. The visual-field deficit seen with monocular viewing is greatest with nasal fixation, and head and eye movements cannot totally compensate for this deficit when viewing time is limited. Vision standards that require full visual fields in each eye are more appropriate for occupations in which peripheral visual targets must be identified and visual search time is limited.

Relationship between Fatigue and Functional Visual Field

A vigilance task like driving a vehicle causes eye fatigue. We previously measured the visual search time for a single flashing light out of 101 stimuli after vigilance tasks of various duration. A CRT display was used to generate the stimuli: containing 1 flashing light and 100 steady lights. We found that the longer the vigilance task, the longer the visual search time. We have now investigated the effect of a vigilance task on the functional visual field. We found that a functional visual field gradually narrows as vigilance task is lengthened. This indicates that narrowing of the functional visual field is a factor contributing to eye fatigue and lengthening of the visual search time.

The influence of colour on visual search times in cluttered environments

Fifty subjects participated in a series of visual search tasks where the aim was to explore the influence of colour on visual search times for targets situated in a series of cluttered distractor fields. The results supported previous findings regarding the effect of colour and showed that, even in cluttered environments, certain hues helped in the reduction of search times. The findings also indicated that there were interaction effects between the colour and positioning of the targets in the distractor fields.

Effects of luminance and colour contrast on the search of information on display devices

For black-and-white alphanumeric information, the speed of visual perception decreases with decreasing contrast. We investigated the effect of luminance contrast on the speed of visual search and reading when characters and background differed also with respect to colour. The luminance contrast between background and characters was varied, while colour contrast was held nearly constant. Stimuli with moderate (green/grey) or high colour contrast (green/red or yellow/blue), and three character sizes (0.17, 0.37, and 1.26 deg) were used. Eye movements were recorded during the visual search task. We found that the visual search times, number of eye fixations, and mean fixation durations increased strongly with decreasing luminance contrast despite the presence of colour contrast. The effects were largest for small characters (0.17 deg), but occurred also for medium (0.37 deg), and in some cases for large (1.26 deg) characters. Similarly, reading rates decreased with decreasing luminance contrast. Thus, moderate or even high colour contrast does not guarantee quick visual perception, if the luminance contrast between characters and background is small. This is probably due to the fact that visual acuity (the ability to see small details) is considerably lower for pure colour information than for luminance information. Therefore, in user interfaces, good visibility of alphanumeric information requires clear luminance (brightness) difference between foreground and background.

Sound Localization with Hearing Protectors: Performance and Head Motion Analysis in a Visual Search Task

The effects of hearing protection on sound localization were examined in the context of an auditory-cued visual search task. Participants were required to locate a visual target in a field of 5, 20, or 50 visual distractors randomly distributed throughout ±180° of azimuth and from approximately −70° to +90° in elevation. Four conditions were examined in which an auditory cue, spatially co-located with the visual target, was presented. In these conditions, participants wore (1) earplugs, (2) earmuffs, (3) both earplugs and earmuffs, or (4) no hearing protection. In addition, a control condition was examined in which no auditory cue was provided. Visual search times and head motion data suggest that the degree to which localization cues are disrupted with hearing protection devices varies with the type of device worn. Moreover, when both earplugs and earmuffs are worn, search times approach those found with no auditory cue, suggesting that sound localization cues are nearly completely eliminated in this condition.

Investigating spatial vision and dynamic attentional selection using a gaze-contingent multiresolutional display.

This study examined spatial vision and attentional selection using a gaze-contingent multiresolutional display, with a dynamic, gaze-centered, high-resolution window and lower resolution periphery. Visual search times and eye movements from 15 participants in a 3 x 3 design (Window Radius x Peripheral Resolution) suggest that contrast sensitivity as a function of retinal eccentricity affects attentional selection and visual processing. Smaller windows led to longer search times and shorter saccades; lower peripheral resolution also shortened saccades (all ps < .05) as a result of avoiding fixating degraded areas. Fixation durations, although longer for smaller windows (p < .05), were unaffected by whether the next saccade went within or outside the window. These results are explained through (a) competition among potential saccade targets where above-threshold filtering reduces an object's relative salience and (b) generally disrupted visual processing.

Fluorescent Colored Highway Signs Don't 'Grab' Attention; They 'Guide' It

A novel inattention search paradigm (Mack &amp; Rock, 1998) was used to assess the visual efficiency of fluorescent colored relative to nonfluorescent colored highway signs. Unexpected presentation of a fluorescent colored search target was not accompanied by an improvement in visual search time. However, visual search times improved dramatically once the participants developed the expectancy that the target feature would be presented on a fluorescent colored singleton. This pattern of results suggests that many of the visibility advantages attributed to the use of fluorescent colors in safety applications may be mediated by top-down attentional mechanisms rather than bottom-up (preattentive) mechanisms as previously assumed.

The role of visual search in the design of effective soft keyboards

As portable, handheld computing devices become more common, alternatives to traditional keyboards must be explored. These alternatives must be compact, lightweight and sufficiently efficient to support the users' tasks. One alternative is the use of small physical keyboards or soft keyboards presented on touch-sensitive surfaces. Many alternative layouts have been explored, including the QWERTY, Dvorak, telephone and various alphabetic organizations. Soukoreff and MacKenzie proposed a model to predict typing times for alternative layouts, but have experienced limited success matching their predictions to observed performance. This paper proposes a revision of the visual search component of their model that considers the familiarity of the organization and the number of letters represented by each key. Results are reported of an experiment that supports the claim that both familiarity and the number of letters per key must be considered when predicting visual search times for alternative keyboard layouts.

Visual search for single and combined features by children and adults: possible developmental inferences.

Visual search time was measured in four groups of children 4 to 10 years of age and in young adults, as a function of display size for both target present and target-absent conditions. The slopes of regression lines in a simple search (search for \ within /) were compared with those obtained in within-dimension conjunction target searches, within either homogeneous (search for the inverted T within Ts) or heterogeneous distractors (search for arrow within Ys and inverted Ys). Analysis indicated that simple search was always preattentive (slopes near 0) after 5 years of age and serial (with positive slopes) before this age. Searching within heterogeneous distractors apparently involved element-by-element scrutiny and focal attention in all groups whereas searching within homogeneous distractors required distributed attention, perhaps based on parallel grouping of distractors in adults, though distractors were focally attended to by children.