Demand Characteristics, Not Effort: The Role Of Backpacks In Judging Distance

Document Type

Poster Session

Publication Date


Published In

Journal Of Vision


Does wearing a backpack increase perceived distance, or does it simply encourage subjects to increase numerical estimates? We first administered a questionnaire to students describing an experiment in which subjects were required to wear a backpack while making distance judgments. Nine of 14 subjects stated the “correct” (signed) hypothesis; the other five made an unsigned prediction. This indicates that the backpack hypothesis is transparent. We next manipulated the transparency of the manipulation. Subjects (N = 68) made distance judgments in a virtual hallway viewed through a head-mounted display. In the explicit burden condition subjects were told they would be wearing a heavy backpack while making distance judgments. In the implicit condition, the same heavy backpack was worn, but it was described as being part of the equipment necessary to operate the virtual reality (indeed the video box for the HMD was inside the backpack). A no-backpack control condition was also run. Because subjects made judgments in two different virtual environments, we expected that people in the control and implicit conditions would believe that the experiment concerned possible differences between the two environments. However, we expected people in the explicit backpack condition to believe that they were to judge distances as farther than they were. Based on an earlier replication of the backpack experiment outdoors with a male experimenter, we only expected to find evidence of demand compliance among women subjects. This prediction was borne out: Only female subjects in the explicit heavy-backpack condition showed an increase in distance estimates. Wearing a heavy backpack that was described as part of the VR equipment had no effect. We conclude that effects of backpacks on judgments of distance are probably due exclusively to demand characteristics and not to any actual change in perception when burdened.


Vision Sciences Society Eighth Annual Meeting

Conference Dates

May 9-14, 2008

Conference Location

Naples, FL