Hadas Marciano

Degraded stimulus visibility and the effects of perceptual load on distractor interference.

In this study we examined whether effects of perceptual load on the attentional selectivity are modulated by degradation of the visual input. According to the perceptual load theory, increasing task difficulty via degradation of stimulus visibility should not alter the typical effect of perceptual load. In previous studies only the target was degraded, resulting in increased distractor saliency. Here we combined manipulation of perceptual load with a more systematic degradation of visual information. Experiment 1 included five conditions. Three conditions involved low perceptual load + contrast reduction of: (A) only the target; (B) only the distractor; (C) both target and distractor. The other two conditions included non-degraded stimuli with low or high perceptual load. In Experiment 2 visibility degradation was established via manipulation of exposure duration. It included two exposure durations—100 and 150 ms—for each load level (low vs. high). The results of both experiments demonstrated reliable distractor interference of a similar magnitude with both degraded and non-degraded stimuli. This finding suggests that task difficulty, when manipulated via degradation of stimulus visibility, does not play a critical role in determining the efficiency of the attentional selectivity. However, contrary to the predictions of the perceptual load theory, in both experiments distractor interference emerged under the high load condition. In Experiment 2 the high-load interference was of the same magnitude as that of the low load condition. This high-load interference is not due to the presence of a mask (Experiment 3) or a mixed design (Experiment 4). These findings suggest that perceptual load may also play a lesser role in attentional selectivity than that assigned to it by the perceptual load theory.

Perceptual Load in Different Regions of the Visual Scene and Its Relevance for Driving

Objective: The aim of this study was to better understand the role played by perceptual load, at both central and peripheral regions of the visual scene, in driving safety. Background: Attention is a crucial factor in driving safety, and previous laboratory studies suggest that perceptual load is an important factor determining the efficiency of attentional selectivity. Yet, the effects of perceptual load on driving were never studied systematically. Method: Using a driving simulator, we orthogonally manipulated the load levels at the road (central load) and its sides (peripheral load), while occasionally introducing critical events at one of these regions. Results: Perceptual load affected driving performance at both regions of the visual scene. Critically, the effect was different for central versus peripheral load: Whereas load levels on the road mainly affected driving speed, load levels on its sides mainly affected the ability to detect critical events initiating from the roadsides. Moreover, higher levels of peripheral load impaired performance but mainly with low levels of central load, replicating findings with simple letter stimuli. Conclusion: Perceptual load has a considerable effect on driving, but the nature of this effect depends on the region of the visual scene at which the load is introduced. Application: Given the observed importance of perceptual load, authors of future studies of driving safety should take it into account. Specifically, these findings suggest that our understanding of factors that may be relevant for driving safety would benefit from studying these factors under different levels of load at different regions of the visual scene.

Perceptual load in central and peripheral regions and its effects on driving performance: advertizing billboards

A broadened version of the perceptual load model was utilized to explore systematically the influence of four variables on drivers behavior: a. levels of load on the road; b. levels of load at the sides of the road; c. events initial location (on the road vs. at the sides of the road); and d. the presence and size of advertizing billboards. 18 participants participated in two experimental sessions in a driving simulator. One of the sessions contained advertizing billboards and the other session did not. The results indicated that billboards can have a considerable effect on various aspects of driving like the time required responding to a potentially dangerous event or simply the number of accidents occurring during driving, but importantly the effect of billboards on driving was modulated by the levels of perceptual load.

Large inter-individual and intra-individual variability in the effect of perceptual load

This study examined whether the recurrent difficulty to replicate results obtained with paradigms measuring distractor processing as a function of perceptual load is due to individual differences. We first reanalyzed, at the individual level, the data of eight previously reported experiments. These reanalyses revealed substantial inter-individual differences, with particularly low percentage of participants whose performance matched the load theory’s predictions (i.e., larger distractor interference with low than high levels of load). Moreover, frequently the results were opposite to the theorys predictions–larger interference in the high than low load condition; and often a reversed compatibility effect emerged–better performance in the incompatible than neutral condition. Subsequently, seven observers participated in five identical experimental sessions. If the observed inter-individual differences are due to some stable trait or perceptual capacity, similar results should have emerged in all sessions of a given participant. However, all seven participants showed large between-sessions variations with similar patterns to those found between participants. These findings question the theoretical foundation implemented with these paradigms, as none of the theories suggested thus far can account for such inter- and intra-individual differences. Thus, these paradigms should be used with caution until further research will provide better understanding of what they actually measure.

The effect of billboard design specifications on driving: A pilot study

Decades of research on the effects of advertising billboards on road accident rates, driver performance, and driver visual scanning behavior, has produced no conclusive findings. We suggest that road safety researchers should shift their focus and attempt to identify the billboard characteristics that are most distracting to drivers. This line of research may produce concrete guidelines for permissible billboards that would be likely to reduce the influence of the billboards on road safety. The current study is a first step towards this end. A pool of 161 photos of real advertising billboards was used as stimuli within a triple task paradigm designed to simulate certain components of driving. Each trial consisted of one ongoing tracking task accompanied by two additional concurrent tasks: (1) billboard observation task; and (2) circle color change identification task. Five clusters of billboards, identified by conducting a cluster analysis of their graphic content, were used as a within variable in one-way ANOVAs conducted on performance level data collected from the multiple tasks. Cluster 5, labeled Loaded Billboards, yielded significantly deteriorated performance on the tracking task. Cluster 4, labeled Graphical Billboards, yielded deteriorated performance primarily on the color change identification task. Cluster 3, labeled Minimal Billboards, had no effect on any of these tasks. We strongly recommend that these clusters be systematically explored in experiments involving additional real driving settings, such as driving simulators and field studies. This will enable validation of the current results and help incorporate them into real driving situations.

The effects of the reliability of an automatic target recognition system on image analyst performance

Motivation -- To study the effects of the reliability of ATR (Automatic Target Recognition) designations on the performance of expert image analysts of SAR (Synthetic Aperture Radar) images. Research approach -- A psychophysical study of the performance of 12 expert analysts of SAR images. Findings -- Analyst performance was influenced by ATR reliability. Higher reliabilities yielded higher hit rates and higher false alarm rates, and low reliabilities the opposite results. This and a signal detection theory analysis indicate that ATR reliability affects the response criterion and not performance per se. (But see Discussion). Research Implications -- The fact that the reliability of items designated by the ATR system affected the criterion of the analysts has important implications. The tendency to mark more items that were designated by the ATR as being true targets should improve the overall performance of analysts working with state-of-the-art ATR systems (see Discussion). Originality/Value -- The research systematically manipulated the reliability levels of simulated ATR systems, and measured their influence on the performance of human analysts. In this context reliability rate means what percentage of the designated items by an ATR system are actually correct targets. Each ATR block was coupled with a similar non-ATR block, a design that aimed to extract the added value of the ATR system to the performance of the human analysts. In addition, a complete within subjects design was used. This procedure provided a good basis for comparing the different conditions in the experiment. Take away message -- While developing an ATR system, one should provide the image analysts with valid assessments of the systems reliability.

The effects of time limitations on target identification

Motivation -- Aiming at making image interpretation more efficient, we studied the effects of limiting exposure durations on performance. Research approach -- Two psychophysical experiments were performed examining the performance of 36 expert image analysts. The targets were presented at three image quality levels. Findings -- The results suggest that limiting the exposure duration of an image to four seconds does not impair the performance of the analysts, i.e., four seconds suffice for identification in an the image interpretation task, no matter what the quality of the image. Research Implications -- This finding suggests that limiting the exposure duration during actual image interpretation would be beneficial since it would shorten the total amount of time needed for interpretation while not lowering the probability of correct identification. Take away message -- Sometimes unlimited time is not necessary in order to obtain the best results. When someone is an expert at what s/he does, making a quick decision might yield equivalent outcomes