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.