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Perceiving slope: With the body or with the eyes?
For the archival version of this research, and the preferred citation, see:
- Weisberg, S. M., Nardi, D. N., Newcombe, N. S., & Shipley, T. F. (2014). Up by upwest: Is slope like north? Quarterly Journal of Experimental Psychology, 67(10), 1959-1976. [DOI]
- Readers also may be interested in similar work with children:
Holmes, C., Nardi, D. N., Newcombe, N. S., & Weisberg, S. M. (2015). Children's Use of Slope to Guide Navigation: Sex Differences Relate to Spontaneous Slope Perception. Spatial Cognition & Computation: An Interdisciplinary Journal, 15(3), 170-185. [DOI]
As humans, we rely on many different types of cues to successfully navigate around our environment. Completing even an everyday task like getting to the grocery store requires using cues in the environment to determine the first direction to walk. For example, you might remember to walk toward the deli while keeping the post office on your right. This process, establishing a position and direction in space, is called reorientation. Some cues, like tall buildings, are primarily visual, while others, like sloped terrain, provide multi-modal information. Accordingly, slope can be used as a reorientation cue (i.e., the grocery store is downhill and to the right). Using a stable cue like slope is ecologically adaptive, as terrain is unlikely to change drastically.
Studies have shown that, indeed, human and non-human animals can use this cue successfully for reorientation and navigation (Miniaci, Scotto, & Bures, 1999; Restat, Steck, Mochnatzki, & Mallot, 2004). Unlike other cues, slope is not only seen and processed visually, but also has a kinesthetic component. We are able to feel slope with our feet and body position in space. Previous research has not addressed which type of sensory information is important, and how that information (visual and kinesthetic) is integrated. In fact, the kinesthetic sense has largely been ignored in human navigation research; a surprising oversight given the ecological relevance and importance of feeling how one moves through space (e.g., Klatzky, Loomis, Beall, Chance, & Golledge, 1998).
Humans can easily perceive slope visually (Proffitt, Bhalla, Gossweiler, & Midgett, 1995) and can use slope to reorient when both visual and kinesthetic cues are available, but men perform significantly better than women (Nardi, Newcombe, & Shipley, 2011). Although sex differences are not uncommon in spatial navigation tasks (e.g., Chai & Jacobs, 2009, Galea & Kimura, 1993), previous research has not addressed whether such sex differences may be accounted for by a female bias for visual cues (or a male bias for kinesthetic cues). The study presented here addresses two main questions. First, are certain types of sensory cues more important in using slope to reorient? Second, are there gender differences in the types of cues used?
We designed a study based on the paradigm of Nardi et al. (2011), described in a previous SILC Showcase (July 2009). Participants entered a square, curtained room with four identical bowls, one in each corner. All features of the room rendered each corner identical to all others, with the exception of the floor which was tilted 5o (see Figure 1). The general procedure was this: for each trial, participants were shown a dollar bill that was hidden under one of the bowls. Their job was to remember where it was and point to it after being blindfolded and disoriented on a swivel chair. Each participant completed one practice trial followed by four test trials.
Participants were randomly assigned to one of three sensory modality conditions: visual, kinesthetic, or visual + kinesthetic. In the visual condition, participants could see where the target was hidden, but were never allowed to stand up (on the chair they could not feel the slope with their feet). In the kinesthetic condition, participants stood up but remained blindfolded, feeling where the target was hidden with a three-foot pole. Finally, in the visual + kinesthetic condition, participants stood up and took off their blindfold – this condition uses the full set of sensory cues available in natural conditions. Encoding time was measured as the amount of time participants took to learn where the target was after they were shown where it was hidden. After this encoding phase, the participant was disoriented by being spun slowly in a chair with a blindfold on while performing a shadowing task (e.g., “Count backwards from 350 by 3.”) After a few spins, the chair stopped and the experimenter placed a pointer in the participant’s lap, and said “Point to where the target is.You are facing downhill (or uphill).” Reaction time and accuracy were recorded (reaction time was measured by how long the participant took to respond after being told which direction he was facing).
During encoding, participants took the most time per trial to learn where the target was hidden in the kinesthetic condition (M = 30.22 seconds), less time in the visual condition (M = 21.86 seconds), and the least time in the visual + kinesthetic condition (M = 17.21 seconds). Figure 2 demonstrates the difference in encoding time. Encoding the goal location in the kinesthetic condition took significantly longer time compared to visual + kinesthetic conditions F(2, 45) = 4.75, p = .01. There was no gender effect for encoding, and no interaction between gender and condition. This result was expected, and can be explained by the uneasiness of moving blindfolded in order to encode the goal relative to the slope of the floor. The interesting result is that the encoding time is not significantly different between the visual and visual + kinesthetic conditions, suggesting that the contribution of kinesthesia to slope perception at encoding is not critical.
Next, we considered accuracy between conditions. When both visual and kinesthetic cues were available, men made an error 15.6% of the time, while women made an error 28.1% of the time. Although this difference was not statistically significant, it shows a trend in agreement with the female difficulty in using slope found in our previous study (Nardi et al., 2011). However, comparing the error rates for the two conditions in which only one cue was available, revealed a significant interaction between sex and condition F(1, 28) = 5.66, p = .03. Men made fewer errors than women when only the kinesthetic cue was available, but made more errors when only the visual cue was available (see Figure 3). This finding suggests that the modality in which slope is encoded has different implications for males and females. The sex-specific advantage with vision for females and with kinesthesia for males indicates possibly different sensory attunements for the perception of a tilted floor – this might underlie sexually dimorphic representations of a goal location on a slope.
♦ Chai, X. J. & Jacobs, L. F. (2009). Sex difference in directional cue use in a virtual landscape. Behavioral Neuroscience, 123, 276–283. doi:10.1037/a0014722.
♦ Galea, L. A. & Kimura, D. (1993). Sex differences in route-learning. Personality and Individual Differences, 14, 53–65. doi:10.1016/0191-8869(93)90174-2.
♦ Klatzky, R. L., Loomis, J. M., Beall, A. C., Chance, S. S. & Golledge, R. G. (1998). Spatial updating of self-position and orientation during real, imagined, and virtual locomotion. Psychological Science, 9, 293-298.
♦ Miniaci, M. C., Scotto, P. & Bures, J. (1999) Place navigation in rats guided by a vestibular and kinesthetic orienting gradient. Behavioural Neuroscience, 113, 1115–1126.
♦ Nardi, D., Newcombe, N. S. & Shipley, T. F. (2011). The world is not flat: Can people reorient using slope? Journal of Experimental Psychology: Learning, Memory, and Cognition, 37, 354–367.
♦ Proffitt, D. R., Bhalla, M., Gossweiler, M. & Midgett, J. (1995). Perceiving geographical slant. Psychonomic Bulletin & Review, 2, 409–428.
♦ Restat, J. D., Steck, S. D., Mochnatzki, H. F. & Mallot, H. A. (2004). Geographical slant facilitates navigation and orientation in virtual environments. Perception, 33, 667–687.