The Establishment Process Of Ground Reference Frame-Evidence From Eye Movement

Spatial perception is one of the important research topics in psychology.The processing of spatial perceptual background is an important branch in this field.He et al.(2004)propose the(sequential-surface-integration-process)SSIP hypothesis based on the view that the ground is important(Gibson,1950)and considered tha ground is important.In the process of spatial perception,individuals first process ground within2-3m,and then use it as a template,with the same texture gradient and continuous surface as conditions,and then gradually integrate the whole ground from near to far to form a complete ground representation.There are researches about SSIP hypothesis,mainly through the perception of egocentric distance.Previous studies mainly interfere with the process of egocentric distance observationand destroy the connection between near ground and far ground.The results show that the binocular system needs continuous surface and the same texture gradient conditions when establishing ground reference frame.But the experimental manipulation and logic are not direct enough,we will use eye movement technology as a more direct means to investigate the establishment process of ground reference frame.In order to further verify and improve SSIP hypothesis,we divided the surface into five regions by eye tracking technology,combined with the blinding walking paradigm and perceptual matching paradigm,then directly investigated the processing process of ground reference frame.In Experiment 1,we discussed how the binocular system established ground reference frame when observing the egocentricdistance in the natural enviroment and in the condition of height.By setting the egocentric distance at four levels and using the blind walking paradigm,the process of building ground reference frame in the process of egocentric distance perception was investigated.The behavior results showed that in the natural enviroment,the subjects judged the egocentricdistance accurately;the eye movement results showed that the time to first fixationindex showed that the time to first fixation about the groundnear the target was the shortest,and the time to first fixation about the ground that near the subject was the longest;the total fixation time index showed that the total fixation time about the ground that near the target was the longest,and the total fixation time about the ground that near the subject was the shortest,so the result of Experiment 1 shows that when the binocular system establishes ground reference frame in the environment with the target,it starts from the ground near the target to observes,it means that observers scaned the ground is from far to near.Eye height can affect the judgment of distance.The results of Experiment 1 may be due to height.Adult’s height is an important clue to obtain spatial information.Both eyes can locate space by the angle declination below the horizon.Therefore,when the subject is in the condition of height,both eyes can quickly obtain the surface information by the angle declination below the horizon.Therefore,it is possible that ground reference frame has been established before the observation of egocentric distance.Therefore,experiment 2 uses the perceptual matching paradigm,by asking the subjects to stand on different heights of shelves to observe the egocentric distance in natural enviroment,the behavioral results show that under the condition of not height,the subjects’ perception of the egocentric distance is different at different levels,and the perceptual distance of the nearest and farthest distance levels tends to compress to the middle;the eye movement results are the same as experiment 1,first observe the ground close to the target,and then observe the ground close to both eyes which is from far to near.Althoughegocentric distance is the main way to test SSIP hypothesis,it is not indicated in SSIP hypothesis that the establishment of ground reference frame needs the existence of the target,so the environment with or without the target also needs to be discussed.So Experiment 3 used the perceptual matching task to investigate the construction process of ground reference frame when the subjects were observing a space without target.The subjects were asked to observe a space without target and track the construction process of ground reference frame in this process.Through the analysis of the eye movement index at the time to first fixation,it is found that in the non target environment,the observation of the subjects starts from the middle region,then from the middle region to the far region,back to the near region,and then back to the far region.Experiment 4 and Experiment 3 were set up in the same way.The establishment of ground reference frame in non height environment was investigated.The time to first fixation and total fixation time were analyzed.The results showed that the two eyes firstly observed the middle region,then looked to the far region,then returned to the middle region,and finally looked to the near region.In a word,the four experiments systematically investigated the process of ground reference frame from the two perspectives of whether there is a target or not and whether it is a height condition,and directly verified SSIP hypothesis by tracking the process,which confirmed the importance of the surface,however,the processing order is different from SSIP hypothesis.Our research has found that in the process of judging egocentric distance in a target environment,the establishment of ground reference frame starts from ground near the target,from far to near;in the process of space observation without a target environment,the establishment of ground reference frame is starting from the middle of the ground.