Dela Cruz Jayrell222

Attention capacity and task difficulty in visual search Liqiang Huang, Harold Pashler* Department of Psychology 0109, University of California, San Diego, La Jolla, CA 92093, USA Received 11 June 2004; accepted 27 June 2004 Abstract When a visual search task is very difficult (as when a small feature difference defines the target), even detection of a unique element may be substantially slowed by increases in display set size. This has been attributed to the influence of attentional capacity limits. We examined the influence of attentional capacity limits on three kinds of search task: difficult feature search (with a subtle featural difference), difficult conjunction search, and spatial-configuration search. In all 3 tasks, each trial contained sixteen items, divided into two eight-item sets. The two sets were presented either successively or simultaneously. Comparison of accuracy in successive versus simultaneous presentations revealed that attentional capacity limitations are present only in the case of spatialconfiguration search. While the other two types of task were inefficient (as reflected in steep search slopes), no capacity limitations were evident. We conclude that the difficulty of a visual search task affects search efficiency but does not necessarily introduce attentional capacity limits. Methods of participants Eight subjects were paid to participate in this study. All had normal vision, and none were aware of the purpose of this study. Stimuli were presented on a high-resolution color monitor. Responses were recorded from two adjacent keys using a standard keyboard. The subjects viewed the displays from a distance of about 60 cm. Procedure Each trial began with a small green fixation cross presented in the center of the screen. Subjects were instructed to fixate the cross, which remained present for 400 ms. The cross was followed by a short blank interval (400 ms), which was then followed by the first display. In a speeded search block, each display remained until the subject responded. In an SIM display, the entire display was presented for certain stimulus duration and then replaced by the mask. In an SUCC display, the two sub-displays were presented successively. Each sub-display was individually and locally masked after a stimulus duration equal to that of a SIM display. The interval between the first and second subdisplays was 500 ms, and the duration of the mask was 100 ms. The stimulus duration was adjusted for each session to get appropriate accuracy levels (mean stimulus durations were as follows: for feature search, 164 ms; for cojunction search, 146 ms; for spatial configuration search, 189 ms). These adjustments were conducted using a staircase: two successive correct responses led to a 1/11 decrease of stimulus duration; one erroneous response led to a 1/10 increase, with the restriction that the stimulus duration was never greater than 250 ms.

Results and Discussion Our results suggest that although the difficulty of a search task (similarity between target and distractors) determines search slopes, substantial slopes do not always indicate the presence of an attentional capacity limit. Singleton and feature conjunction searches can show little attentional capacity limitation even when the tasks are very difficult by the standard criteria (e.g. Treisman & Gelade, 1980). It seems, therefore, that attention capacity is not affected by search task efficiency, but rather is determined mainly by the nature of the task. Unlimited-capacity processing that is fast and efficient in easy tasks, when faced with harder tasks, may become slow, inefficient, and perhaps inaccurate, but it still fails to show an attentional capacity limitation (i.e. the processing of different parts of the display may be slow or inaccurate, but it is still independent of processing in other parts of the display.) It should be noted that the RT slope of spatial configuration search (48 ms/item) is greater than that of tasks 1 (35 ms/item) and 2 (39 ms/item). This fact points to one conceivable objection to our above interpretation: it is possible that the influence of an attentional capacity limit is determined by difficulty (search slope) in a highly non-linear fashion; perhaps we see no influence in tasks 1 and 2 only because their efficiency is less than some threshold reflecting the point where attentional capacity limits come into play (e.g. a search slope over 40 ms/item). This explanation, though not impossible, appears, unlikely, since naturally the intercept of attention capacity vs. slope function should be zero if the attentional capacity limit effect monotonically increases with the slope (the attention capacity should be non-zero when the slope is non-zero). Another conceivable objection is that the search might have no attention capacity limit when the set size is smaller than a certain number, but still show attention capacity limits when the set size exceeds that number (see, e.g. Pashler, 1987, for a related suggestion). The current results may be explained by assuming that the number is greater than 16 for feature search but smaller than 16 for spatial-configuration search. While this interpretation cannot be ruled out, it seems somewhat implausible. Reference: Carter, R. C. (1982). Visual search with color. Journal of Experimental Psychology: Human Perception and Performance, 8, 127–136. Carter, E. C., & Carter, R. C. (1981). Color and conspicuousness. Journal of Optical Society of American, 71, 723–729. Duncan, J. (1980). The demonstration of capacity limitation. Cognitive Psychology, 12, 75–96. Duncan, J., & Humphreys, G. W. (1989). Visual search and stimulus similarity. Psychological Review, 96, 433– 458.

Effect of Template Complexity on Visual Search and Dual-Task Performance Patrick A. Bourke1 and John Duncan2 1University of Lincoln, Lincoln, United Kingdom, and 2MRC Cognition and Brain Sciences Unit, Cambridge, United Kingdom ABSTRACT

Even dissimilar tasks interfere with one another when done together. We used visual search to examine the underlying cause of such interference. In many models, visual search is a process of biased competition controlled by a template describing the target to be sought. When the display is processed, matching against this template guides attention to the target. We show that increasing template complexity increased interference with a dissimilar concurrent task, story memory. This result was independent of reaction time: Increases in template complexity were associated with no increase in search time in Experiment 1 and with a decrease in search time in Experiment 2. The results show that the dual-task demands of visual search reflect the complexity of the template used in task control, and that this factor can be isolated from other sources of difficulty. Method of participants Sixty-four participants were tested, 16 in each of four conditions. Participants were first- and second-year undergraduate psychology students, predominantly female, with a modal age of 19. They participated for participant-pool credit, a voluntary system that allows subsequent use of the pool. They were not informed of the purpose of the experiment and were unfamiliar with the story that was played for the memory task, as well as with the visual search tasks used. Procedure In each of the three visual search tasks, the participant had to decide if the letter L was present. This target was present on 50% of the trials. The target could occur at one of eight positions evenly spaced on the perimeter of an imaginary circle that was centered on a fixation cross and had a radius of approximately 5.41. In the first task, participants had to decide if a target letter L was present in a display that could consist of eight Os or seven Os and an L. Conventionally, this is considered a feature search task, because any of several single features (e.g., curvature, closure) can be used to distinguish targets from distractors. In the second task, only a single L was presented on each trial, and participants had to decide whether the letter was the target, an L in its correct orientation, or a distractor, an L that had been rotated 901 to the left or to the right. Results and Discussion The most striking aspect of the results is that the effect of the manipulations on reaction time was not reflected in the effects on dual-task performance. First, feature search and conjunction-without-distractors search did not differ in reaction times (or number of trials presented), but there was a significant decrement in dual-task performance for conjunction-without distractors search relative to feature search. Second, reaction times were significantly longer for conjunction-with distractors search than for conjunctionwithout-distractors search, but dual-task performance did not differ between these two conditions.

Reference: Bourke, P.A. (1997). Measuring attentional demand in continuous dual-task performance. The Quarterly Journal of Experimental Psychology, 50A, 821–840. Bourke, P.A., Duncan, J., & Nimmo-Smith, I. (1996). A general factor in dual task performance decrement. The Quarterly Journal of Experimental Psychology, 49A, 525– 545. Bundesen, C. (1990). A theory of visual attention. Psychological Review, 97, 523–547. Cave, K., & Wolfe, J. (1990). Modelling the role of parallel processing in visual search. Cognitive Psychology, 22, 225–271. Dehaene, S., Kerszberg, M., & Changeux, J.P. (1998). A neuronal model of a global workspace in effortful cognitive tasks. Proceedings of the National Academy of Sciences, USA, 95, 14529–14534.

Do New Objects Capture Attention? Steven L. Franconeri,1 Andrew Hollingworth,2 and Daniel J. Simons3 1Harvard University, 2University of Iowa, and 3University of Illinois Abstract The visual system relies on several heuristicsto direct attention to important locations and objects. One of these mechanisms directs attention to sudden changes in the environment. Although a substantial body of research suggests that this capture of attention occurs only for the abrupt appearance of a new perceptual object, more recent evidence shows that some luminance-based transients (e.g., motion and looming) and some types of brightness change also capture attention. These findings show that new objects are not necessary for attention capture. The present study tested whether they are even sufficient. That is, does a new object attract attention because the visual system is sensitive to new objects or because it is sensitive to the transients that new objects create? In two experiments using a visual search task, new objects did not capture attention unless they created a strong local luminance transient. Methods of participant Thirty-two University of Iowa undergraduates voluntarily participated in exchange for course credit or pay. They reported normal or corrected-to-normal vision. All stimuli were displayed on a 17-in. video monitor operating at 100 Hz. Responses were collected by a serial button box. The experiment was controlled by a Pentium-based computer running E-Prime software. Viewing position was maintained at 80 cm by a forehead rest. The stimuli are illustrated in Figure 1. The background was gray (27.2 cd/m2), and the letters and fixation cross were black (<0.01 cd/m2). Results and Discussion Trials with response times greater than 3 s or less than 200 ms were removed from the analysis (less than 1% of all trials). The mean error rate was 1.4%, and the error rate was not greater than 2.3% in any condition. Accuracy data for each condition were again submitted to a 2 _ 3 ANOVA with new-letter type(target, distractor) and set size as factors. In the control condition, observers were more accurate when the new letter was the target than when it was a distractor, F(1, 31) 5 6.7, p 5 .015. As in Experiment 1, newletter type did not interact with set size in either condition, both Fs(2, 62) < 1.4, ps > .25, ruling out any speed-accuracy trade-offs. Reference: Abrams, R.A., & Christ, S.E. (2003). Motion onset captures attention. Psychological Science, 14, 427–432.

Visual Search Does Not Remain Efficient When Executive Working Memory Is Working Sang-Hoon Han and Min-Shik Kim Yonsei University, Seoul, Korea Abstract Working memory (WM) has been thought to include not only short-term memory stores but also executive processes that operate on the contents of memory. The present study examined the involvement of WM in search using a dual-task paradigm in which participants performed visual search while manipulating or simply maintaining information held in WM. Experiments 1a and 2a involved executive WM tasks that required counting backward from a target digit and sorting a string of letters alphabetically, respectively. In both experiments, the search slopes in the dual-task condition were significantly steeper than those in a search-alone condition, indicating that performing the WM manipulation tasks influenced the efficiency of visual search. In contrast, when information was simply maintained in WM (Experiments 1b and 2b), search slopes did not differ between the single- and dual-task conditions. These results suggest that WM resources related to executive functions may be required in visual search. Method of participants Forty undergraduate students (10 in each experiment) at Yonsei University, Korea, participated for course credit, after giving informed consent. All had normal or correctedto-normal vision. None knew the purpose of the experiment or the expected result. Procedure Figure 1 illustrates the procedures in all four experiments. At the beginning of the dual-task condition (memory and search) in Experiment 1a, a random three-digit number was presented at the center of the display. In memory, participants were required to count backward from that number by 3s. For the first 4 s, they performed this memory manipulation task alone, and then a visual search array was presented. Participants were required to use their left hand to make a speeded response to this array while they continued to count backwards. The index or middle finger was used to press the ‘‘S’’ or ‘‘X’’ keyon the computer keyboard to indicate the presence of a top-gap or bottom-gap target, respectively. The search array was presented until participants responded. A 1-s blank period followed. Then the instruction message for the memory test (‘‘Write down the number you just calculated’’) was presented until participants finished writing down the number that they just had in memory. The next trial started when participants pressed the space bar. Results and Discussion In this experiment, the participants were required to actively manipulate a memory stimulus in the dual-task condition. Search slopes were significantly steeper in this condition than in the search-alone condition, indicating that performing a WM task influenced the efficiency of visual search. Our results contrast with those of Woodman et al. (2001), suggesting that WM plays an important role in visual search and that there is a close link between WM and attention. That is, WM resources, especially resources involving executive functions, seem to be required in visual search. Reference:

Awh, E., Jonides, J., & Reuter-Lorenz, P. (1998). Rehearsal in spatial working memory. Journal of Experimental Psychology: Human Perception and Performance, 24, 780–790. Baddeley, A.D. (1992). Working memory. Science, 255, 556–559. Brainard, D.H. (1997). The Psychophysics Toolbox. Spatial Vision, 10, 443–446. Bundesen, C. (1990). A theory of visual attention. Psychological Review, 97, 523–547. Cave, K.R., & Wolfe, J.M. (1990). Modeling the role of parallel processing in visual search. Cognitive Psychology, 22, 225–271.

Independent Processing of Parts and of Their Spatial Organization in Complex Visual Objects Martin Arguin1 and Daniel Saumier1,2 Abstract A visual search experiment using synthetic three-dimensional objects is reported. The target shared its constituent parts, the spatial organization of its parts, or both with the distractors displayed with it. Sharing of parts and sharing of spatial organization both negatively affected visual search performance, and these effects were strictly additive. These findings support theories of complex visual object perception that assume a parsing of the stimulus into its higher-order constituents (volumetric parts or visible surfaces). The additivity of the effects demonstrates that information on parts and information on spatial organization are processed independently in visual search. Methods of participant Twelve students from the University of Montreal, Canada, took part in the experiment. All had normal or corrected visual acuity, and they were naive as to the purpose of the experiment. Procedure Subjects were instructed to indicate, on every trial, whether a particular target object was present (50% of trials) in a display of a variable number of items. On targetpresent trials, the two relevant distractors were replicated an equal number of times. We maintained constant display size across target-present and target-absent trials by presenting an unequal number of replications of the two distractors on target-absent trials. For these trials, one distractor was replicated one more time than the other, with the two distractors occurring an equal number of times within each block. Results and Discussion The sharing of parts and the sharing of spatial organization between the target and distractors both affected visual search performance. Most important, these effects were strictly additive. Part and spatialorganization sharing both resulted in increased RTs, as well as in increased slopes of RTs as a function of the number of items displayed. These findings have important implications with respect to the processes involved in the perception of complex visual objects in the context of speeded visual tasks such as visual search. Reference: Arguin, M., Bub, D., & Dudek, G. (1996). Shape integration for visual object recognition and its implication in category-specific visual agnosia. Visual Cognition, 3, 221–275. Arguin, M., & Leek, E.C. (2003). Orientation-invariance in visual object priming depends on prime-target asynchrony. Perception & Psychophysics, 65, 469–477. Arguin, M., & Saumier, D. (2000). Conjunction and linear non-separability effects in visual shape encoding. Vision Research, 40, 3099–3115. Biederman, I. (1987). Recognition by components: A theory of human image understanding. Psychological Review, 94, 65–96.

Stimulus-driven attentional capture: An empirical comparison of display-size and distance methods Massimo Turatto and Giovanni Galfano University of Trento, Rovereto, Italy Simona Gardini and Gian Gastone Mascetti University of Padua, Italy Abstract Subjects performed a visual search task for a vertical-target line embedded among tilted-distractor lines, presented inside 4, 8, or 12 coloured discs. Interestingly, when the colour singleton was task irrelevant, and data were analysed by means of the display-size method combined with the zero-slope criterion, no evidence for attentional capture by colour was found. However, when data were analysed by means of the distance method, which consists of monitoring the spatial relationship between the target and the singleton, results showed that the target was found faster and/or more accurately when it was inside the singleton than when it was in a nonsingleton location. This provided evidence for a stimulus-driven attentional capture. In addition, the application of signal detection methodology showed that attentional capture, as revealed by the distance method, resulted from a perceptual modulation at the singleton location, rather than from a criterion shift. We conclude that, at least with the kind of stimuli used here, the displaysize method combined with the zero-slope criterion is less than ideal for investigating how static discontinuities can affect the automatic deployment of visual attention. Methods of participant A total of 28 subjects (6 male and 22 female) from the University of Padua served as subjects (age range 20–29 years). All had normal or corrected-to-normal visual acuity and were unaware of the purpose of the experiment. Procedure Trials began with a fixation point presented for 500 ms, then the visual search display was turned on and displayed only for 180 ms, rendering any eye movements useless. From visual-search display onset, subjects had 2500 ms for responding. Half of the subjects responded to target present with the left hand (“Q” key), and to target absent with the right hand (“P” key), and the remainders vice versa. The feedback for the incorrect responses was a 500-ms, 500-Hz tone, presented together with the message “error”. If a response was not produced within 2500 ms, the same sound signal, along with the display message “missed response”, was presented. Subjects were told to be as accurate as possible in making their responses. Results and Discussion This experiment had the purpose of making a direct comparison between the display-size method and the distance method in their capability to reveal a stimulusdriven attentional capture by a colour singleton. In this regard, the results were very interesting, revealing that if subjects’ performance was monitored by means of the display-size method, no evidence of attentional capture emerged. Reference: Bacon, W. F., & Egeth, H. E. (1994). Overriding stimulus-driven attentional capture. Perception and Psychophysics, 55, 485–496.