Mental rotation within linguistic and non-linguistic domains in users of American sign language

Abstract

American sign language (ASL) uses space itself to encode spatial information. Spatial scenes are most often described from the perspective of the person signing (the 'narrator'), such that the viewer must perform what amounts to a 180 degrees mental rotation to correctly comprehend the description. But scenes can also be described, non-canonically, from the viewer's perspective, in which case no rotation is required. Is mental rotation during sign language processing difficult for ASL signers? Are there differences between linguistic and non-linguistic mental rotation? Experiment 1 required subjects to decide whether a signed description matched a room presented on videotape. Deaf ASL signers were more accurate when viewing scenes described from the narrator's perspective (even though rotation is required) than from the viewer's perspective (no rotation required). In Experiment 2, deaf signers and hearing non-signers viewed videotapes of objects appearing briefly and sequentially on a board marked with an entrance. This board either matched an identical board in front of the subject or was rotated 180 degrees. Subjects were asked to place objects on their board in the orientation and location shown on the video, making the appropriate rotation when required. All subjects were significantly less accurate when rotation was required, but ASL signers performed significantly better than hearing non-signers under rotation. ASL signers were also more accurate in remembering object orientation. Signers then viewed a video in which the same scenes were signed from the two perspectives (i.e. rotation required or no rotation required). In contrast to their performance with real objects, signers did not show the typical mental rotation effect. Males outperformed females on the rotation task with objects, but the superiority disappeared in the linguistic condition. We discuss the nature of the ASL mental rotation transformation, and we conclude that habitual use of ASL can enhance non-linguistic cognitive processes thus providing evidence for (a form of) the linguistic relativity hypothesis.