Reading direction influences lateral biases in letter processing.

Humans have a limited capacity to identify concurrent, briefly presented targets. Recent experiments using concurrent rapid serial visual presentation of letters in horizontally displaced streams have documented a deficit specific to the stream in the right visual field. The cause of this deficit might be either prioritization of the left item based on participants' experience reading from left to right, or a right-hemisphere advantage specific to dual stimulation. Here we test the reading-experience hypothesis by using participants who have experience reading both a language written left-to-right (English) and one written right-to-left (Arabic). When tested with English letters, these participants showed a deficit, of a similar magnitude to that found previously, for reporting the item on the right. However, when the stimuli were Arabic letters the deficit was absent. This suggests that reading direction plays a large role in the second-target deficit. The pattern of participants' errors suggests where in the processing stream reading experience affects stimulus processing: Specifically, the error pattern suggests that the limited-capacity stage responsible for the deficit corresponds to a postsampling process such as consolidation into short-term memory. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Implied reading direction and prioritization of letter encoding.

Capacity limits hinder processing of multiple stimuli, contributing to poorer performance for identifying two briefly presented letters than for identifying a single letter. Higher accuracy is typically found for identifying the letter on the left, which has been attributed to a right-hemisphere dominance for selective attention. Here, we use rapid serial visual presentation (RSVP) of letters in two locations at once. The letters to be identified are simultaneous and cued by rings. In the first experiment, we manipulated implied reading direction by rotating or mirror-reversing the letters to face to the left rather than to the right. The left-side performance advantage was eliminated. In the second experiment, letters were positioned above and below fixation, oriented such that they appeared to face downward (90° clockwise rotation) or upward (90° counterclockwise rotation). Again consistent with an effect of implied reading direction, performance was better for the top position in the downward condition, but not in the upward condition. In both experiments, mixture modeling of participants' report errors revealed that attentional sampling from the two locations was approximately simultaneous, ruling out the theory that the letter on one side was processed first, followed by a shift of attention to sample the other letter. Thus, the orientation of the letters apparently controls not when the letters are sampled from the scene, but rather the dynamics of a subsequent process, such as tokenization or memory consolidation. Implied reading direction appears to determine the letter prioritized at a high-level processing bottleneck. (PsycINFO Database Record

Velocity of motion across the skin influences perception of tactile location.

We investigated the influence of motion context on tactile localization, using a paradigm similar to the cutaneous rabbit or sensory saltation (Geldard FA, Sherrick CE. Science 178: 178-179, 1972). In one of its forms, the rabbit stimulus consists of a tap in one location quickly followed by another tap elsewhere, creating the illusion that the two taps are near each other. Instead of taps, we used position of a halted brush and instead of distance judgment, localization responses. The brush moved across the skin of the left forearm, creating a clear motion signal before and after a rabbitlike leap of 10 cm (at 100 cm/s). Three before-and-after velocities (7.5, 15, or 30 cm/s) were used. Participants (n = 13) pointed with their right arm at the felt location of the brush when it halted either 1 cm before or after the leap. These stops were 12 cm apart, but distances computed from localization responses were only 5.4, 6.5, and 7.5 cm for the three velocities, respectively (F[2,11] = 15.19, P = 0.001). Thus the leap resulted in compressive position shift, as described previously for sensory saltation, but modulated by motion velocity before the leap: the slower the motion, the greater the shift opposite to motion direction. No gap in stimulation was perceived. We propose that velocity extrapolation causes the position shift: extrapolated motion does not have enough time to bridge the real spatial gap and thus assigns a closer location to the skin on the opposite side of the gap.