Multiple groups of orientation–selective visual mechanisms underlying rapid orientated–line detection

Abstract

Visual search for an edge or line element di¡ering in orientation from a background of other edge or line elements can be performed rapidly and e¡ortlessly. In this study, based on psychophysical measurements with ten human observers, threshold values of the angle between a target and background line elements were obtained as functions of background-element orientation, in brief masked displays. A repeated-loess analysis of the threshold functions suggested the existence of several groups of orientation-selective mechanisms contributing to rapid orientated-line detection; speci¢cally, coarse, intermediate and ¢ne mechanisms with preferred orientations spaced at angles of approximately 90 , 35 ^50 and 10 ^25 , respectively. The preferred orientations of coarse and some intermediate mechanisms coincided with the vertical or horizontal of the frontoparallel plane, but the preferred orientations of ¢ne mechanisms varied randomly from observer to observer, possibly re£ecting individual variations in neuronal sampling characteristics.

Evidence against global attention filters selective for absolute bar-orientation in human vision

“…A target bar of a given orientation pops out from a field of distractor bars of some other fixed orientation provided the difference in orientation between target and distractor bars is large enough (Beck & Ambler, 1973;Foster & Ward, 1991a;, 1998Nothdurft, 1991Nothdurft, , 1992Nothdurft, , 1993Nothdurft, , 1994Sagi & Julesz, 1985;Treisman, 1985;Treisman & Souther, 1985;Wolfe et al, 1992). This frequently replicated result might be taken to suggest that human vision possesses a number (perhaps a continuum) of mechanisms selective for different orientations.…”

“…Although the research of Foster and colleagues (Foster & Ward, 1991a, 1991bFoster & Westland, 1998) seems to suggest the existence in human vision of mechanisms selective for different absolute orientations, it is important to note that Foster's experiments involve participants looking for the existence of a unique bar-one that differs from everything around it. Participants are not made aware before each trial of the orientation of the target bar, so they are not attending to any one specific orientation.…”

“…Under the model (elaborated in detail by , it is the relative activation produced by the target versus distractor bars rather than the difference in activation that is the crucial factor controlling performance in the classification task. Foster and Westland (1998) investigated whether human vision possesses orientation-selective mechanisms more finely tuned than those discovered by Foster & Ward (1991a). Foster and Westland (1998) used displays similar to those used by Foster and Ward (1991a) again measuring threshold values of the angle between a target and background bar elements as a function of background-element orientation.…”

“…Foster and Westland (1998) investigated whether human vision possesses orientation-selective mechanisms more finely tuned than those discovered by Foster & Ward (1991a). Foster and Westland (1998) used displays similar to those used by Foster and Ward (1991a) again measuring threshold values of the angle between a target and background bar elements as a function of background-element orientation. This time, however, they measured the angular increment threshold across a more finely sampled domain of angles: θ = 0, 5, … 175 deg.…”

“…The work of Foster and colleagues (Foster & Ward, 1991a, 1991bFoster & Westland, 1998) suggests that human vision possesses an ensemble of mechanisms selective for different absolute orientations. Other research, however, both psychophysical (Nothdurft, 1991(Nothdurft, , 1992(Nothdurft, , 1993(Nothdurft, ,1994Koene & Li, 2007;Sagi & Julesz, 1985) and neurophysiological (Kastner, Nothdurft & Pigarev, 1999;Nothdurft, Gallant & Van Essen, 1999, 2000Schofield & Foster, 1995;Van Essen et al, 1989) suggests that human vision possesses at least one mechanism sensitive to Borientation contrast^(as opposed to absolute orientation).…”