Wednesday, February 10, 2021

Zygmunt Pizlo, Philosophizing cannot substitute for experimentation: comment on Hoffman, Singh & Prakash (2014)

 Zygmunt Pizlo:  “I am an “expert” on 3D shape perception, so I will confine my comments about veridicality to shape. Unlike Hoffman et al., I do not have the temerity required to discuss veridicality in vision in general, as well as in smell, taste, touch and hearing in such varied species as humans, bees, and spiders.”

“… Any contemporary use of a Motor Theory of Perception, and this includes Hoffman et al.’s explanation of 3D shape perception, can be viewed as a legacy of psychology’s Dark Age called “Radical Behaviorism”. This is precisely what Hoffman et al. are offering us. As for me, “no, thank you very much.”

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Zygmunt Pizlo’s paper does a wonderfully concise job of bringing Hoffman’s “veridicality” challenge back down to Earth and our three dimensional world.  This paper was 1200 words long and I whittled to 500 some odd.  Please visit the complete article for all the details. 


Philosophizing cannot substitute for experimentation: comment on Hoffman, Singh & Prakash (2014)

  • Zygmunt Pizlo, September 18, 2015 

Psychonomic Bulletin & Review

volume 22, pages 1546–1547 (2015)



Abstract  

The perception of a 3D shape must be excluded from Hoffman et al.’s “interface theory” primarily because shape is characterized by its symmetries. When these symmetries are used as a priori constraints, 3D shapes are always recovered from 2D retinal images veridically. 


These facts make it clear that 3D shape perception is completely different from, as well as more important than, all other perceptions because the veridicality of our perception of 3D shapes (and 3D scenes) accounts for our successful adaptation to the natural environment.


… when we talk about veridical 3D perception, we are referring to our natural visual space, that is, a space with natural, symmetrical objects residing, as they naturally do, on a common ground because of gravity. 


The concept of an “empty” visual space, used in laboratories, that contains only a few isolated points of light in total darkness, or a few objects floating in the air, no matter how attractive mathematically, is actually empty from an empirical, as well as from a computational, point of view. …


Note that the concept of a priori constraints is largely ignored by Hoffman et al. Their neglect of such potentially critical factors allows them …


There is absolutely nothing in the literature to justify such a view. Quite the opposite is true: there is overwhelming evidence showing that 3D vision, but not the taste sweetness, is treated as an inverse problem by the perceptual system and is solved as such (Pizlo, 2001; Poggio et al., 1985).


With this said, I will continue my comment by pointing out that the veridicality of visual perception is an empirical question, and visual psychophysics has advanced to the point that we have at hand, and have already used, all of the tools required to answer this question. Speculation about this now is pointless. 


Several relatively sophisticated experiments on how people see 3D shapes have provided a convincing positive answer to the veridicality question (Pizlo et al., 2010). …


Ideally, they would stay away from it completely because continuing to fuss about veridicality can only muddy the waters. 


It would really be a shame to do this now because it took such a long time to separate the wheat from the chaff in the long history of research on shape perception: this took at least 300 years (Pizlo, 2008). 


The fact that we see symmetrical shapes as symmetrical means that we see them veridically, and if an object is not exactly symmetrical, like a chair with a broken leg, we see it as a symmetrical object with one broken part. If this is not veridicality, what is?


I have been presenting such “symmetry” arguments periodically to the authors of the target paper since 2009. 


It was already obvious to me back then that their interface theory does not apply to shape perception, no matter how well it applied elsewhere, but they simply could not put their theory aside. 


They did recognize that shape and symmetry made trouble for it, and the only way they could keep applying their non-veridicality theory to the perception of symmetrical shapes was to claim that it is not our perceptions, but our actions that are symmetrical. 



Any contemporary use of a Motor Theory of Perception, and this includes Hoffman et al.’s explanation of 3D shape perception, can be viewed as a legacy of psychology’s Dark Age called “Radical Behaviorism”. 


This is precisely what Hoffman et al. are offering us. As for me, “no, thank you very much.”

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