Visual search and mouse-pointing in labeled versus unlabeled two-dimensional visual hierarchies

An experiment investigates (1) how the physical structure of a computer screen layout affects visual search and (2) how people select a found target object with a mouse. Two structures are examined---labeled visual hierarchies (groups of objects with one label per group) and unlabeled visual hierarchies (groups without labels). Search and selection times were separated by imposing a point-completion deadline that discouraged participants from moving the mouse until they found the target. The observed search times indicate that labeled visual hierarchies can be searched much more efficiently than unlabeled visual hierarchies, and suggest that people use a fundamentally different strategy for each of the two structures. The results have implications for screen layout design and cognitive modeling of visual search. The observed mouse-pointing times suggest that people use a slower and more accurate speed-accuracy operating characteristic to select a target with a mouse when visual distractors are present, which suggests that Fitts' law coefficients derived from standard mouse-pointing experiments may under-predict mouse-pointing times for typical human-computer interactions. The observed mouse-pointing times also demonstrate that mouse movement times for a two-dimensional pointing task can be most-accurately predicted by setting the w in Fitts' law to the width of the target along the line of approach.