Subitizing And Counting: Preattentive And Attentive Processing In Visual Enumeration

Subitizing, the process of visual enumeration when there are fewer than four items, is rapid (40-100 msec/item), accurate and effortless. In contrast, counting, the process of enumerating more than four items is comparatively slow (250-350 msec/item), effortful and error prone. Why does this occur? In this paper an attempt is made to incorporate subitizing and counting into a general theory of visual perception and spatial attention, as espoused by Marr(1982), Ullman(1984), and Treisman(1988). In particular, it is argued that the rapid apprehension of number in the 1-4 range is parasitic on a preattentive limited capacity mechanism that individuates feature clusters by assigning spatial reference tokens or FINSTs to them(Pylyshyn, 1989). These spatial reference tokens permit the identities of a small number of items to be maintained though their properties and retinal coordinates change, a capability important for directing the attentional focus and coordinating eye and hand movements. If the subitizing process makes use of such preattentive information, then it should not be possible to subitize when spatial attention is required to compute spatial relations, resolve the item as a whole or discern items to be counted from other distractor items. Thus, it was predicted that the slope of the latency function in the 1-4 range should approximate that of the 5+ range if spatial attention is required to perform a particular enumeration task. In contrast, it was predicted that subitizing should be possible when preattentive information could be used to distinguish the items to be counted from one another, or from other distractor items. Therefore, it was predicted that there should be discontinuities in slopes of the latency function between the 1-4 and 5+ range, as shown by deviations from linearity in trend analysis.;Five experiments were performed. In the first, subjects were shown capable of subitizing when the task was to enumerate items of a particular colour though they were not capable of subitizing when the task was to enumerate items that were connected to each other by a contour. This result was expected because spatial attention is presumed necessary to compute the connected relation(Ullman, 1984; Jolicoeur, 1988). The second pair of experiments showed that though subjects can easily subitize when items are defined by groups of contours instead of simple edge points, they cannot easily enumerate such items if they are concentric, as would be predicted given that preattentive grouping processes would cluster all the contours into a unit in this case. The fourth and fifth experiments show that subjects can subitize certain target items in a field of distractors, but only if the property that differentiates targets from distractors is a feature, or a property thought to emerge preattentively. In situations where attention is required to form a unified object description by joining different dimensions (e.g., colour and orientation), or by joining different parts of an item (e.g., an O and a stem to form a Q), subitizing was not apparent. Overall, these experiments suggest that the subitizing process relies on preattentive information

How Missing a Treatment of Mixed Amphetamine Salts Extended Release Affects Performance in Teen Drivers with ADHD

Mixed Amphetamine Salts Extended Release (MAS-XR or Adderall XR®) is a stimulant medication used to control symptoms of ADHD. People occasionally fail to take their medications. The goal of this pilot study was to assess the impact of a single missed medication on driving performance in 14 teen drivers with ADHD mixed type as a function of driving skill. A double-blind placebo control crossover design was used and participants were tested in a driving simulator. On the evening of the first day, baseline measures of driving performance were taken to assess driving skills (on medication). Then on two consecutive days drivers were tested three times a day, one day on medication and the other day off. Results indicated increased collisions and hazard response time off medication, with performance worst on 36 hours post-medication. Participants with the least developed driving skills benefited most from medication. This highlights the importance of consistent medication use in inexperienced teen drivers with ADHD

Effect of Driving Experience on Change Detection Based on Target Relevance and Size

Earlier studies that investigated the effects of driving experience and target safety relevance on change detection have produced conflicting results. Using a flicker change detection task to investigate the effect of driving experience on the ability to detect changes in objects that vary in safety relevance and size, the present study attempted to clarify some controversies by addressing three important methodological issues. The data showed that experienced drivers exhibited more efficient selection strategies than novice drivers and thus may have more spare resources to analyze less relevant objects in the driving environment. Selection strategies for relevant information appear to be sensitive to object size whereas selection of irrelevant information is downgraded comparatively and unaffected by size. Findings are discussed as they relate to theoretical and practical implications

The Effects of Task Load and Vehicle Heterogeneity on Performance in the Multiple-Vehicle Tracking Task

When crossing traffic at busy intersections, drivers must keep track of the changing positions of cyclists, pedestrians and other vehicles to avoid collision. Multiple-object tracking is the ability to monitor the positions of a number of selected moving objects (targets) among others (distractors) in a complex scene. Most young adults can track 3-5 items at once but older adults cannot track as many, a finding that may partially explain older drivers’ increased risk at intersections. Because tracking represents an important component of driving, a variant of the multiple-object tracking task called multiple-vehicle was created to measure tracking performance in a driving simulator. However, it is unclear whether tracking while driving works the same as tracking carried out on its own. Laboratory studies suggest that tracking improves when the moving items are heterogeneous, and on the road, it is far more typical that vehicles differ from one another rather than being all the same. Drivers were given the task of tracking the positions of 4 vehicles in a field of 8 on a highway, and the effects of task load (tracking alone, tracking while driving) on tracking performance were measured as a function of whether the target and distractor vehicles were homogeneous. Steering and headway maintenance variability were also assessed. The results indicated that heterogeneity only enabled better tracking when drivers were tracking in isolation. Heterogeneity had no significant effect on tracking when participants were tracking while driving though it did significantly reduce their steering variability

Quantifying the influence of bars on action-based dynamical modelling of disc galaxies

Action-based dynamical modelling, using stars as dynamical tracers, is an excellent diagnostic to estimate the underlying axisymmetric matter distribution of the Milky Way. However, the Milky Way's bar causes non-axisymmetric resonance features in the stellar disc. Using Roadmapping (an action-based dynamical modelling framework to estimate the gravitational potential and the stellar distribution function), we systematically quantify the robustness of action-based modelling in the presence of a bar. We construct a set of test-particle simulations of barred galaxies (with varying bar properties), and apply Roadmapping to different survey volumes (with varying azimuthal position, size) drawn from these barred models. For realistic bar parameters, the global potential parameters are still recovered to within ${\sim \! 1 \! - \! 20}$ percent. However, with increasing bar strength, the best-fit values of the parameters progressively deviate from their true values. This happens due to a combination of radial heating, radial migration, and resonance overlap phenomena in our bar models. Furthermore, the azimuthal location and the size of the survey volumes play important roles in the successful recovery of the parameters. Survey volumes along the bar major axis produce larger (relative) errors in the best-fit parameter values. In addition, the potential parameters are better recovered for survey volumes with larger spatial coverage. As the Sun is located just ${\sim \! 28 \! - \! 33}$ degrees behind the bar's major axis, an estimate for the bar-induced systematic bias -- as provided by this study -- is therefore crucial for future modelling attempts of the Milky Way.Comment: 18 pages, 10 figures, 2 tables, comments are welcom

Manipulating Drive Characteristics to Study the Effects of Mental Load on Older and Younger Drivers

A driving simulator was used to assess performance in younger and older drivers (M ages 18 and 71 years). The impacts of three challenges were assessed: visibility (clear day, fog), traffic density (low, high) and wayfinding (no challenge, drivers challenged to use signs and landmarks to find their destination). Performance was measured in terms of hazard RT, collisions, wayfinding errors (missed or extra turns), and driving speed. The challenge manipulations produced interactive effects and age was a factor in some of these interactions. Older drivers missed more turns in wayfinding but overall they performed as well or better than younger drivers and reduced their speed more to driving challenges

Relative importance of dispersion and rate-limited mass transfer in highly heterogeneous porous media: Analysis of a new tracer test at the Macrodispersion Experiment (MADE) site

This is the published version. Copyright American Geophysical Union[1] A single-well injection-withdrawal (SWIW) bromide tracer test was conducted to further investigate transport processes at the Macrodispersion Experiment (MADE) site on Columbus Air Force Base in Mississippi. The bromide breakthrough curve is highly asymmetric and exhibits an early time high-concentration peak followed by an extended period of low-concentration tailing. Comparisons of results simulated by advection-dispersion (AD) and dual-domain mass transfer (DDMT) models with the field data show that the DDMT model more accurately represents the magnitudes of both the early high-concentration peak and the later low-concentration tail. For both the AD and DDMT models, the match with field data is enhanced by incorporating hydraulic conductivity information from new direct-push profiling methods. The Akaike information criterion for the DDMT models is much smaller than that for the AD models in both the homogeneous and heterogeneous cases investigated in this work. The improved match of the DDMT model with the SWIW test data supports the hypothesis of mass transfer processes occurring at this highly heterogeneous site

A 2.75-Approximation Algorithm for the Unconstrained Traveling Tournament Problem

A 2.75-approximation algorithm is proposed for the unconstrained traveling tournament problem, which is a variant of the traveling tournament problem. For the unconstrained traveling tournament problem, this is the first proposal of an approximation algorithm with a constant approximation ratio. In addition, the proposed algorithm yields a solution that meets both the no-repeater and mirrored constraints. Computational experiments show that the algorithm generates solutions of good quality.Comment: 12 pages, 1 figur