Animals are remarkably skilled in their capacity to use a range of environmental features to orient in space once they have lost track of where they are, a process called reorientation . Among the types of cues that animals can use, one that has received little attention is the directional information extractable from a surface extending in the vertical dimension, such as a geographical slant or slope (Restat, Steck,
Mochnatzki, & Mallot, 2004; Miniaci, Scotto, & Bures, 1999; Proffitt,
Bhalla, Gossweiler & Midgett, 1995).
Slope is a perceptually salient cue because it provides potentially redundant, multimodal sensory activations, such as visual, proprioceptive, kinesthetic and vestibular stimuli. However, studies have shown that the conscious awareness of slope seems to be highly variable, depending, for example, on physiological and psychosocial resources (Proffitt, Bhalla, Gossweiler & Midgett, 1995; Schnall, Harber,
Stefanucci & Proffitt, 2008).
The present research aimed to study, for the first time in a real-world environment, the extent to which humans can use a geographical slant for successful reorientation and goal location.
The enclosure was completely symmetrical and featureless, and no external cue could be seen or heard (participants wore earphones). Therefore, the only way to encode and locate the goal was using the slope gradient, i.e., encoding the goal with respect to the vertical and orthogonal (left-right) axes of the slope (e.g., the target is in the upper-left bowl; see Fig. 2).
•Training was composed of 4 trials, with the target always in the same place.
•Subjects were given feedback and shown the target at the end of the trial.
•On each trial subjects started facing a different side of the enclosure.
Fig. 2
Fig. 3
Participant
Fig. 1 PVC pipe frame
Wooden platform
Acute
Obtuse
The experimental enclosure consisted of a square, wooden platform with a PVC pipe frame on top (overall size of the enclosure: base, 244 x 244 cm; height, 206 cm; see Fig.1-3). Curtains were placed around and on top of the PVC frame, such that the experimental environment was completely enclosed. The enclosure could be placed horizontally on the floor, or could be tilted to a 5 ° inclination. Illumination was provided by four 25-W lamps on the platform, one in each corner. Four red bowls, used as potential hiding places for the target, were located in the corners. A swivel chair was placed in the center of the enclosure (even when the enclosure was slanted, the chair’s axis of rotation was always perpendicular to the earth).
20 males and 20 females took part to the experiment. The enclosure was slanted with a 5 ° inclination. The participant saw the experimenter hide the target (a $1 bill) under one of the four bowls. Then the participant was blindfolded and spun on the swivel chair for 1 minute. During this time, the experimenter moved around the curtains so that subjects could not use the wrinkles to determine the goal location. After being disoriented, participants had to tell where the target was hidden.
20
Fig. 5
Number of correct
As expected, when tested on a
18 choices during the tests.
flat surface (i.e., without any cue),
16
14
12
Males participants were disoriented and could not locate the correct corner
10
8
Females more than by chance. However, when tested on the slope, both
6
Chance males and females performed
4
2
0 significantly above chance
(binomial test, males: p < .0001;
Flat Slope females: p < .05).
These results rule out the possibility that participants were using cues other than the slope to solve the task. Only when the enclosure was slanted could subjects reorient and successfully locate the target.
Fig. 6
Participant self-report strategy use.
Bowl
Slope
Other
View-based
More males than females reported using slope to locate the target,
Fisher’s exact test, p < .05. This suggests that males outperform females because they are more likely to use slope to solve the task.
Subjects left the enclosure and came back two times for the tests (one trial each, with no feedback). Tests were presented in counterbalanced order.
Flat test . For one trial the enclosure was placed horizontally on the floor →
No polarizing cues were available that would enable to distinguish a specific corner → Expected performance is at chance (25%).
Slope test. For one trial the enclosure was tilted again at a 5 ° inclination →
Participants could now locate the target.
Male scores in the waterlevel task were significantly higher than female’s, t (38) = 2.13, p < .05. There was a significant correlation between water-level and slope task performance, r(38) = .36, p < .05. However, when controlling for gender, the correlation was not significant, r(37) = .22, p = .18. This suggests that water-level and slope task performance correlate because males are better than females in both tasks.
2.0
1.5
1.0
0.5
0.0
4.0
3.5
3.0
2.5
At the end of the experiment subjects completed the water-level task (Piaget &
Inhelder, 1956) and reported what information they used to locate the target:
-Slope (using the slope gradient)
-Other (using path integration or any feature cues, e.g., wrinkles in the curtains)
-View-based (using the different angle of incidence between the uphill and downhill curtains with the platform).
Fig. 4
Males
Mean correct choices (
Chance
Females
± SD) during the 4 training trials.
Both genders performed above chance, males: t (19) = 14.33, p < .0001; females: t (19) = 2.41, p < .05.
However, males performed substantially and significantly better than females, t (38)
= 4.43, p < .0001. This effect size is large, d = 1.4, with means differing for more than
1 SD.
Both males and females are able to use the slope of the floor to reorient and locate a hidden goal. However, there is a large gender difference in performance because females are less likely to spontaneously use slope cues than males.
Males also outperform females in the water-level task, and a similar result has been shown in other visual perception tasks that require engaging the horizontal-vertical reference frame ( Linn & Peterson, 1985 ). However, the present finding is important because it shows a male superiority in the use of a multimodal cue in which kinesthetic and vestibular information – as opposed to visual information – play a crucial role.
Future research will have to investigate the factors underlying the gender difference in slope use, and whether this female deficit might be eliminated by drawing more attention to the fact that the floor is tilted.