The extent of crowding in peripheral vision does not scale with target size

Abstract

Identifying a target is more difficult when distracters are present within a zone of interaction around the target. We investigated whether the spatial extent of the zone of interaction scales with the size of the target. Our target was a letter T in one-of-four orientations. Our distracters were four squared-thetas in one-of-two orientations, presented one in each of the four cardinal directions, equidistant from the target. Target-distracter separation was varied and the proportion of correct responses at each separation was determined. From these the extent of interaction was estimated. This procedure was repeated for different target sizes spread over a 5-fold range. In each case, the contrast of the target was adjusted so that its visibility was constant across target sizes. The experiment was performed in the luminance domain (grey targets on grey background) and in the chromatic domain (green target on equiluminant grey background). In the luminance domain, target size had only a small effect on the extent of interaction; these interactions did not scale with target size. The extents of interaction for chromatic stimuli were similar to those for luminance stimuli. For a fixed target visibility, decreasing the duration of the stimulus resulted in an increase in the extent of interaction. The relevance of our findings is discussed with regard to a variety of proposed explanations for crowding. Our results are consistent with an attention-based explanation for crowding.

The relative benefit of word context is a constant proportion of letter identification time

“…The stimuli in Bouma's (1970) study were not scaled for eccentricity, whereas the stimuli used here were. This may account for our different results, since Strasburger et al (1991) have found that both the size of the flank and its distance from the target affect crowding (although see Tripathy & Cavanagh, 2002, for data that suggest otherwise).…”

“…Although SD threshold is an unusual method for determining visual crowding, it may be better than the typical method of measuring percentage correct for a fixed SD. In a recent study in which SD was varied, Tripathy and Cavanagh (2002) found different degrees of crowding, depending on SD. In their study, the change in SD was used to equate performances for individual targets.…”

“…Visual crowding is a form of lateral masking that refers specifically to the reduced perceptibility of letters when they are surrounded by other letters (Chung, Levi, & Legge, 2001). Although this definition of crowding is by no means universal (e.g., Cavanagh, 2001;Intriligator & Cavanagh, 2001;Leat, Li, & Epp, 1999;Tripathy & Cavanagh, 2002), it is the one adopted here. Understanding how the perceptibility of letters changes when they are surrounded by other letters is critical to our understanding of such tasks as reading (Bouma, 1970), where the letters that make up words must be identified.…”

The Effect of Aging and Attention on Visual Crowding and Surround Suppression of Perceived Contrast Threshold

“…13,22 One explanation is that crowding is a result of the limitation of the spatial resolution of attention. 23,24 In this model, stimulus features are taken into account and crowding occurs only when flankers share the defining dimension of the target (e.g., color or spatial frequency). Thus, when two or more items are within the smallest possible selected region of attention and share a defining feature, the individual item is not identified.…”

Effects of spatial separation between stimuli in whole report from brief visual displays

“…Thus, Pelli, Palomares, and Majaj (2004) argued that crowding limits all vision and has nothing to do with attention, whereas Strasburger (2005) argued that the impairment of character recognition by crowding is caused, to a large extent, by spatially imprecise focusing of attention (see also He, Cavanagh, & Intriligator, 1996;Intriligator & Cavanagh, 2001;Tripathy & Cavanagh, 2002). For example, in the flanker paradigm used by Bouma (1970) and Strasburger, among others, the observer must discriminate the target (center character) from the distractors (flanker characters).…”