Gravity Influences How We Expect a Cursor to Move

Abstract

We expect a cursor to move upwards when we push our computer mouse away. Do we expect it to move upwards on the screen, upwards with respect to our body, or upwards with respect to gravity? To find out, we asked participants to perform a simple task that involved guiding a cursor with a mouse. It took participants that were sitting upright longer to reach targets with the cursor if the screen was tilted, so not only directions on the screen are relevant. Tilted participants' performance was indistinguishable from that of upright participants when the screen was tilted slightly in the same direction. Thus, the screen's orientation with respect to both the body and gravity are relevant. Considering published estimates of the ocular counter-roll induced by head tilt, it is possible that participants actually expect the cursor to move in a certain direction on their retina.

Keywords: computer mouse; cursor; frames of reference; gravity; pointing/hitting; visually guided movements.

Figure 1.

Participants either sat upright (blue drawings) or tilted 45° to the left on a specially designed chair with a surface supporting the left side of their body and surfaces for their feet and the mouse that were also tilted by 45° (red drawings). In each case the screen was tilted either −90°, −45°, 0°, or 45° with respect to the participant's body. Data points show the mean and 95% confidence intervals across the 27 participants’ median values for each condition. The green arrow illustrates the condition in which the participant was tilted but the screen was aligned with gravity (see screen orientation in drawing).