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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.


Summary of mean weber fractions (panel A) and mean JNDs (panel B) of our study and other previous studies that did not control for the size change cue. Red dashed line represents the end of peripersonal space and beginning of action space.
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Figure 6: Summary of mean weber fractions (panel A) and mean JNDs (panel B) of our study and other previous studies that did not control for the size change cue. Red dashed line represents the end of peripersonal space and beginning of action space.

Mentions: The perception of depth depends on the combination of multiple cues, whose reliability changes with the distance of the object to the observers (Gilinsky, 1951; Da Silva, 1985; Nagata, 1991; Landy et al., 1995; Loomis et al., 1996; Loomis and Knapp, 2003; Swan et al., 2007; Armbrüster et al., 2008; Saracini et al., 2009; Naceri et al., 2011). A cue of primary importance is the angular size, defined as the size of the image that an object produces on the retina of the observer. In our study, participants reported on their perceived depth of virtual and real stimuli located in action space, whose angular size was held constant between stimuli. The estimated JND was equal to 0.10 m in the real environment and 0.26 m in the VR setting, corresponding to a Weber fraction of 0.05 and 0.13, respectively. In Figure 6, we compared these values to previous studies in real and virtual environments where the relative change in the angular size across stimuli was not controlled and thus provided a cue to depth (size change cue). The discriminability of our stimuli was markedly worse, showing the important role of the size change cue in the tested range. This is further discussed in the following paragraph.


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)

Summary of mean weber fractions (panel A) and mean JNDs (panel B) of our study and other previous studies that did not control for the size change cue. Red dashed line represents the end of peripersonal space and beginning of action space.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: Summary of mean weber fractions (panel A) and mean JNDs (panel B) of our study and other previous studies that did not control for the size change cue. Red dashed line represents the end of peripersonal space and beginning of action space.
Mentions: The perception of depth depends on the combination of multiple cues, whose reliability changes with the distance of the object to the observers (Gilinsky, 1951; Da Silva, 1985; Nagata, 1991; Landy et al., 1995; Loomis et al., 1996; Loomis and Knapp, 2003; Swan et al., 2007; Armbrüster et al., 2008; Saracini et al., 2009; Naceri et al., 2011). A cue of primary importance is the angular size, defined as the size of the image that an object produces on the retina of the observer. In our study, participants reported on their perceived depth of virtual and real stimuli located in action space, whose angular size was held constant between stimuli. The estimated JND was equal to 0.10 m in the real environment and 0.26 m in the VR setting, corresponding to a Weber fraction of 0.05 and 0.13, respectively. In Figure 6, we compared these values to previous studies in real and virtual environments where the relative change in the angular size across stimuli was not controlled and thus provided a cue to depth (size change cue). The discriminability of our stimuli was markedly worse, showing the important role of the size change cue in the tested range. This is further discussed in the following paragraph.

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.