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Subitizing, coined in 1949 by E.L. Kaufman et al. refers to the rapid, accurate, and confident judgments of number performed for small numbers of items. The term is derived from the Latin adjective ''subitus'' (meaning "sudden") and captures a feeling of immediately knowing how many items lie within the visual scene, when the number of items present falls within the subitizing range.〔 Number judgments for larger set-sizes were referred to either as counting or estimating, depending on the number of elements present within the display, and the time given to observers in which to respond (i.e., estimation occurs if insufficient time is available for observers to accurately count all the items present). The accuracy, speed, and confidence with which observers make judgments of the number of items are critically dependent on the number of elements to be enumerated. Judgments made for displays composed of around one to four items are rapid, accurate and confident. However, as the number of items to be enumerated increases beyond this amount, judgments are made with decreasing accuracy and confidence.〔 In addition, response times rise in a dramatic fashion, with an extra 250–350 ms added for each additional item within the display beyond about four. While the increase in response time for each additional element within a display is relatively large outside the subitizing range (i.e., 250–350 ms per item), there is still a significant, albeit smaller, increase within the subitizing range, for each additional element within the display (i.e., 40–100 ms per item〔). A similar pattern of reaction times is found in young children, although with steeper slopes for both the subitizing range and the enumeration range. This suggests there is no span of apprehension as such, if this is defined as the number of items which can be immediately apprehended by cognitive processes, since there is an extra cost associated with each additional item enumerated. However, the relative difference in costs associated with enumerating items within the subitizing range are small, whether measured in terms of accuracy, confidence, or speed of response. Furthermore, the values of all measures appear to differ markedly inside and outside the subitizing range.〔 So, while there may be no span of apprehension, there appear to be real differences in the ways in which a small number of elements is processed by the visual system (i.e., approximately less than four items), compared with larger numbers of elements (i.e., approximately more than four items). A 2006 study demonstrated that subitizing and counting are not restricted to visual perception, but also extend to tactile perception, when observers had to name the number of stimulated fingertips. A 2008 study also demonstrated subitizing and counting in auditory perception. Even though the existence of subitizing in tactile perception has been questioned,〔Gallace, A., Tan, H. Z., & Spence, C. (2008). Can tactile stimuli be subitised? An unresolved controversy within the literature on numerosity judgments. Perception, 37(5), 782.〕 this effect has been replicated many times and can be therefore considered as robust. The subitizing effect has also been obtained in tactile perception with congenitally blind adults. Together, these findings support the idea that subitizing is a general perceptual mechanism extending to auditory and tactile processing. ==Enumerating afterimages== As the derivation of the term "subitizing" suggests, the feeling associated with making a number judgment within the subitizing range is one of immediately being aware of the displayed elements.〔 When the number of objects presented exceeds the subitizing range, this feeling is lost, and observers commonly report an impression of shifting their viewpoint around the display, until all the elements presented have been counted.〔 The ability of observers to count the number of items within a display can be limited, either by the rapid presentation and subsequent masking of items, or by requiring observers to respond quickly.〔 Both procedures have little, if any, effect on enumeration within the subitizing range. These techniques may restrict the ability of observers to count items by limiting the degree to which observers can shift their "zone of attention" successively to different elements within the display. Atkinson, Campbell, and Francis demonstrated that visual afterimages could be employed in order to achieve similar results. Using a flashgun to illuminate a line of white disks, they were able to generate intense afterimages in dark-adapted observers. Observers were required to verbally report how many disks had been presented, both at 10 s and at 60 s after the flashgun exposure. Observers reported being able to see all the disks presented for at least 10 s, and being able to perceive at least some of the disks after 60 s. Despite a long period of time to enumerate the number of disks presented when the number of disks presented fell outside the subitizing range (i.e., 5–12 disks), observers made consistent enumeration errors in both the 10 s and 60 s conditions. In contrast, no errors occurred within the subitizing range (i.e., 1–4 disks), in either the 10 s or 60 s conditions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「subitizing」の詳細全文を読む スポンサード リンク
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