Orientation and Direction Parameters

Orientation and Direction Parameters 1. Distinct Representations for Axes and End Points The two parameters ‘‘orientation’’ and ‘‘direction’’ are hierarchical in nature in that orientation corresponds to the assignment of an axis of a reference frame to a particular spatial dimension (horizontal or vertical), whereas direction corresponds to the particular end points of a given axis. Nevertheless, these are distinct parameters that seem to be represented separately. For example, Logan (1995, 1996) used a spatial cuing task in which participants had to report the color of a located object that was indicated by its spatial location with respect to a central reference object. In some conditions, a distractor object appeared at the opposite end point from the located object (e.g., a located object placed above a reference object and a distractor placed below it), and the two objects could be the same color or diVerent colors. This is an interesting comparison because when the objects were the same color, participants only need to compute the orientation of the relevant axis in order to make their judgment. That is, because the end points were the same, they could pick either object and respond correctly, with no need to assign the spatial term to a particular endpoint. However, when the target and distractor diVered in color, participants need to compute both the orientation and the direction in order to access the correct end point and report the correct color. Logan found that response times were significantly faster when the target and distractors were the same color than diVerent colors, indicating that the orientation and direction parameters can be set separately. 144 Laura A. CarlsonConverging evidence for separate representations for direction and orientation comes from research on patients with spatial deficits (McCloskey & Rapp, 2000; HoVman, Landau, & Pagani, 2003). For example, HoVman et al. (2003) observed that patients with Williams syndrome have impaired representation of direction but not axial structure in a block construction task, more often placing blocks at the opposite end point within the correct axis (e.g., below rather than above) than on a diVerent axis (e.g., left rather than above)