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Depth discrimination of constant angular size stimuli in action space: role of accommodation and convergence cues.

Naceri A, Moscatelli A, Chellali R - Front Hum Neurosci (2015)

Bottom Line: We replicated the task in virtual and real environments and we found that the performance was significantly different between the two environments.Whereas, in virtual reality (VR) the responses were significantly less precise, although, still above chance level in 16 of the 20 observers.The values of Weber fractions estimated in our study were compared to those reported in previous studies in peripersonal and action space.

View Article: PubMed Central - PubMed

Affiliation: Department of Cognitive Neuroscience, Cognitive Interaction Technology Center of Excellence (CITEC), Bielefeld University Bielefeld, Germany.

ABSTRACT
In our daily life experience, the angular size of an object correlates with its distance from the observer, provided that the physical size of the object remains constant. In this work, we investigated depth perception in action space (i.e., beyond the arm reach), while keeping the angular size of the target object constant. This was achieved by increasing the physical size of the target object as its distance to the observer increased. To the best of our knowledge, this is the first time that a similar protocol has been tested in action space, for distances to the observer ranging from 1.4-2.4 m. We replicated the task in virtual and real environments and we found that the performance was significantly different between the two environments. In the real environment, all participants perceived the depth of the target object precisely. Whereas, in virtual reality (VR) the responses were significantly less precise, although, still above chance level in 16 of the 20 observers. The difference in the discriminability of the stimuli was likely due to different contributions of the convergence and the accommodation cues in the two environments. The values of Weber fractions estimated in our study were compared to those reported in previous studies in peripersonal and action space.

No MeSH data available.


Stimulus locations and timing. (A) Stimulus lines enumerated from 0 to 8. The black arrow represents the direction of the observer’s view and the green arrow represents the big screen position for the VR setup. Red points represents comparisons and blue points represents standards. (B) Timing during one trial of the standard and comparison located at the same stimulus line.
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Figure 2: Stimulus locations and timing. (A) Stimulus lines enumerated from 0 to 8. The black arrow represents the direction of the observer’s view and the green arrow represents the big screen position for the VR setup. Red points represents comparisons and blue points represents standards. (B) Timing during one trial of the standard and comparison located at the same stimulus line.

Mentions: Before each experiment, the participant’s eye height, eyes distance from the screen and interpupillary distance (IPD) were measured using a digital precision optical instrument. These measurements were used to set the parameters for the VR stimulus presentation. Lighting and shading were held constant for the stimuli presented in VR. In both VR and real objects experiments, participants were presented with a sequence of two spheres, one blue (standard) and one red (comparison) located along the same line in depth (Figure 2A), and then asked to verbally indicate which appeared closer by saying “red” or “blue”. Only one sphere was visible during each presentation interval, with one second pause between the two presentations (Figure 2B). The order of presentation (blue then red, or red then blue) was randomized and repeated 10 times. Each experiment consisted of two 20 min sessions, with a break between sessions. We manipulated both the distance and the angle (azimuth and elevation) at which the spheres were presented in the stimulus pair standard-comparison (Figure 2A illustrates the different angles tested in the experiment).


Depth discrimination of constant angular size stimuli in action space: role of accommodation and convergence cues.

Naceri A, Moscatelli A, Chellali R - Front Hum Neurosci (2015)

Stimulus locations and timing. (A) Stimulus lines enumerated from 0 to 8. The black arrow represents the direction of the observer’s view and the green arrow represents the big screen position for the VR setup. Red points represents comparisons and blue points represents standards. (B) Timing during one trial of the standard and comparison located at the same stimulus line.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4584972&req=5

Figure 2: Stimulus locations and timing. (A) Stimulus lines enumerated from 0 to 8. The black arrow represents the direction of the observer’s view and the green arrow represents the big screen position for the VR setup. Red points represents comparisons and blue points represents standards. (B) Timing during one trial of the standard and comparison located at the same stimulus line.
Mentions: Before each experiment, the participant’s eye height, eyes distance from the screen and interpupillary distance (IPD) were measured using a digital precision optical instrument. These measurements were used to set the parameters for the VR stimulus presentation. Lighting and shading were held constant for the stimuli presented in VR. In both VR and real objects experiments, participants were presented with a sequence of two spheres, one blue (standard) and one red (comparison) located along the same line in depth (Figure 2A), and then asked to verbally indicate which appeared closer by saying “red” or “blue”. Only one sphere was visible during each presentation interval, with one second pause between the two presentations (Figure 2B). The order of presentation (blue then red, or red then blue) was randomized and repeated 10 times. Each experiment consisted of two 20 min sessions, with a break between sessions. We manipulated both the distance and the angle (azimuth and elevation) at which the spheres were presented in the stimulus pair standard-comparison (Figure 2A illustrates the different angles tested in the experiment).

Bottom Line: We replicated the task in virtual and real environments and we found that the performance was significantly different between the two environments.Whereas, in virtual reality (VR) the responses were significantly less precise, although, still above chance level in 16 of the 20 observers.The values of Weber fractions estimated in our study were compared to those reported in previous studies in peripersonal and action space.

View Article: PubMed Central - PubMed

Affiliation: Department of Cognitive Neuroscience, Cognitive Interaction Technology Center of Excellence (CITEC), Bielefeld University Bielefeld, Germany.

ABSTRACT
In our daily life experience, the angular size of an object correlates with its distance from the observer, provided that the physical size of the object remains constant. In this work, we investigated depth perception in action space (i.e., beyond the arm reach), while keeping the angular size of the target object constant. This was achieved by increasing the physical size of the target object as its distance to the observer increased. To the best of our knowledge, this is the first time that a similar protocol has been tested in action space, for distances to the observer ranging from 1.4-2.4 m. We replicated the task in virtual and real environments and we found that the performance was significantly different between the two environments. In the real environment, all participants perceived the depth of the target object precisely. Whereas, in virtual reality (VR) the responses were significantly less precise, although, still above chance level in 16 of the 20 observers. The difference in the discriminability of the stimuli was likely due to different contributions of the convergence and the accommodation cues in the two environments. The values of Weber fractions estimated in our study were compared to those reported in previous studies in peripersonal and action space.

No MeSH data available.