Egocentric Distance Perception On Flat And Uphill Ground

Humans skilfully interact with their environments on a daily basis. Humans are able to locate themselves, navigate in the space around them and develop a mental representation of the environment. All these are further dependent upon our ability to accurately perceive distance. For viewing distances up a hill and viewing distance on flat ground, the geographic slant, one of the principle components of the ground, affords differences in various distance cues. In this research, perception and action tasks were used to investigate whether distances up a hill are perceived differently from those on flat ground.Perception and action tasks are both used to evaluate the egocentric distance perception. One of the problems of the availability of various tasks is subjects' inconsistent performances in different tasks, e.g. difference between verbal report and blind walking task. Some researchers suggested that the different performances reflect the difference between the two visual systems, perception and action visual systems. But other researchers suggested that only a single representation of egocentric distance was achieved from the visual input and then the representation would be transformed independently by the respective response requirements of different tasks. Support for the later note comes from some researches which indicated that change of the calibration of the task led to the change in performance accuracy. The current research examined subjects' performance in visual matching and blind walking tasks on different terrains, to investigate whether the results of the two tasks would covariate under different terrain conditions.It is assumed that there are two phases for each of the visual matching and blind walking tasks, distance presentation phase and distance reproduction phase. In each phase distance is perceived based on different input information. According to the two phases and the two terrains, there are four terrain conditions for each task, flat-flat, flat-hill, hill-flat, hill-hill (in each condition, the former refers the distance presentation terrain, the later refers the distance reproduction terrain).Three experiments were conducted in an outdoor environment in SWU campus with a flat road connected with an uphill road. The roads are both 4m in width and more than 25m in length. The slant of the uphill road is 8 degrees. There is no any auditory localization cues available to subjects.. The target distances used in the three experiments were 6m, 8m, 10m, 12m and 14m.In experiment 1, 24 subjects were separated into two groups to perform blind walking task. While one group of subjects only walked on flat ground by performing in flat-flat and hill-flat conditions; the other group of subjects only walked on uphill ground by performing in flat-hill and hill-hill conditions. The constant error of subjects' walked distance were computed and statistically analyzed. The results showed that for condition of walking on uphill ground, subjects walked significantly longer distance after viewing distances on flat ground than after viewing distances on uphill ground. For condition of walking on flat ground, the walked distances did not differ significantly for the two viewing terrains. For condition of viewing distances on flat ground, subjects walked significantly longer distance when walking on uphill ground than when walking on flat ground. For condition of viewing distance on uphill ground, the walked distance did not differ significantly for the two walking terrains. The part of the results of experiment 1 indicated that distances on uphill ground were perceived relatively shorter than those on flat ground.In experiment 2, 12 subjects performed visual matching task for all four terrain conditions. The constant error of subjects' matched distances were computed and statistically analyzed. The results showed the marginally significant main effect of viewing terrain and significant main effect of matching terrain. Subjects matched relatively shorter distances after viewing distances on uphill ground than after viewmg distances on flat ground. Subjects matched relatively longer distance when matching on uphill ground than when matching on flat ground. The results indicated that the distances on uphill ground were perceived relatively shorter than those on flat ground.In experiment 3, 12 subjects performed visual matching and blind walking tasks for all four terrain conditions. The constant error of subjects' responses were computed and statistically analyzed. The results indicated that there was no significant main effect for task. But there were the significant main effect of viewing terrain and response terrain. Subjects reproduced relatively shorter distances after viewing distances on uphill ground than after viewing distances on flat ground. Subjects reproduced relatively longer distance when making responses on uphill ground than when making responses on flat ground. The results indicated that the distances on uphill ground were perceived relatively shorter than those on flat ground. The results from the two tasks showed the high degree of linear correlation, indicating the tight covariance between the two tasks under different terrain conditions. The results supported the note that the two tasks reflect a single egocentric distance representation.The results of these three experiments indicated that the distances on uphill ground were perceived relatively shorter than those on flat ground. This result is not consistent with the results from other researches. For example, in Stefanucci et al 's research, subjects verbally reported that the distances on a 20 degrees slant were relatively longer than those on flat ground. The difference between these results may be due to the different slant of the uphill ground used in the two researches. The current research used the uphill ground of 8 degrees which is frequently encountered in humans' daily life. While humans may frequently act (like walking) on a uphill ground of 8 degrees, humans seldom act on a uphill ground of 20 degrees. The difference of the results of the two researches may be due to the different slant itself and the consequent difference in the frequency of acting on the different uphill ground.The current research showed the tight covariance between visual matching and blind walking tasks under different terrain conditions, supporting the note that the two tasks reflect a single egocentric distance representation. The current research did not deny the difference between the results of different tasks, e.g. verbal report and blind walking tasks, but just suggested that the difference may be attributable to other variables instead of different distance representation. Some researches indicated that change of the calibration of the task led to the change in performance accuracy. The different performances in tasks may be just due to the different calibration of different tasks. Because visual matching and blind walking tasks may be well calibrated based on daily experience, subjects showed good accuracy in these two tasks. But verbal report seldom calibrated in daily life, so subjects showed large distortion in verbal report task.In three experiments, the current research used visual matching and blind walking tasks to investigate the egocentric distance perception on flat and uphill ground. The results showed that distances on uphill ground were perceived relatively shorter than those on flat ground. The results of the two tasks showed the tight covariance under different terrain conditions, supporting the note that the two tasks reflect a single egocentric distance representation.