Shift Invariance

[Lev Goldfarb]

On Sun, 10 Mar 1996, Edelman Shimon wrote:

> Many thanks to Irv Biederman for posting the details of his findings,
> along with a comparison with the results of Nazir & O'Regan. His
> effort should reduce the chance of the readers of this list jumping to
> premature conclusions.
> 
> Note that the purpose of my previous posting was to advocate caution,
> certainly not to argue that all claims of invariance are wrong.
> Fortunately, my job in this matter is easy: just one example of a
> manifest lack of invariance suffices to invalidate the strong version
> of invariance-based theory of vision, which seems to be espoused by
> Goldfarb:
> 
> > If we 1) DO NOT FORGET that the biological systems have at their disposal
> > quite adequate means to extract symbolic (structural) representation right
> > from the very beginning and 2) FORGET about our inadequate numeric models,
> > then the question would not have arisen in the first place. Symbolic 
> > representations EMBODY shift invariance. 
> 
> So, here it goes... Whereas invariance does hold in many recognition
> tasks (in particular, in Biederman's experiments, as well as in the
> experiments reported in [1]), it does not in others (as, e.g., in [2],
> where interaction between size invariance and orientation is
> reported). A recent comprehensive survey of (the far from invariant)
> human performance in recognizing rotated objects can be found in
> [3]. Furthermore, not only recognition, but also perceptual learning,
> seems to be non-invariant in some cases; see [4,5].
> 
> FORGETTING about experimental findings will not make them go away,
> just as pointing out that symbolic representations EMBODY invariance
> will not make biological vision embrace a symbolic approach if it has
> not done so until now.

It appears that there is a considerable confusion as to what "shift 
invariance" is: shift invariance should not include size,  orientation, or 
context invariance, since an encoding of these may involve additional 
structural information.

(By the way, I do not read Biederman's message as Edelman does)

 -- Lev