Re: Reply to Wolf

feedbackdroid wrote:



There are, as far as I know, no "edge detectors" in human retinas. You
are probably thinking of the so called "simple cells" of the primary
visual cortex (V1, aka "striate cortex", aka "area 17"), some of which,
following the work of Hubel and Wiesel in the 1960's, were thought of for
a while as "edge detectors". By the 1980's the limitations and
inaccuracies of that view had made it untenable, though it lives on in
the imaginations of some individuals, none of them neuroscientists, and
none of them students of (the interdisciplinary topic) vision science.

You might enjoy Helga Kolb's survey article: "How The Retina Works"

http://webvision.med.utah.edu/



The matter may be "closed" in some circles, but if you follow down
the link given, you find .....


.... Selective quotes from material I am thoroughly familiar with, none of
which contradicts in the slightest what I posted. On the contrary, De
Valois, quoted below, did some of the crucial reasearch establishing
systematic variation in *Frequency* *Selectivity*:

De Valois RL, Albrecht DG, Thorell LG. Spatial frequency selectivity of
cells in macaque visual cortex. Vision Res. 1982;22(5):545?559.

=====
We measured the spatial frequency contrast sensitivity of cells in the
primate striate cortex at two different eccentricities to provide
quantitative statistics from a large population of cells. Distributions of
the peak frequencies and bandwidths are presented and examined in
relationship to (a) each other, (b) absolute contrast sensitivity, (c)
orientation tuning, (d)retinal eccentricity, and (e) cell type. Simple and
complex cells are examined in relationship to linear/nonlinear (that is,
X/Y) properties; a procedure is described which provides a simple, reliable
and quantitative method for classifying and describing striate cells. Among
other things, it is shown that (a) many stirate cells have quite narrow
spatial bandwidths and (b) at a given retinal eccentricity, the
distribution of peak frequency covers a wide range of frequencies; these
findings support the basic multiple channel notion. The orientation tuning
and spatial frequency tuning which occurs at the level of striate cortex
(in a positively correlated fashion) suggests that the cells might best be
considered as two-dimensional spatial filters.
=====

http://www.ncbi.nlm.nih.gov/sites/entrez?db=PubMed&cmd=Retrieve&list_uids=7112954

Proc Natl Acad Sci U S A. 1989 January; 86(2): 711?715.
Spatial-frequency organization in primate striate cortex.
M S Silverman, D H Grosof, R L De Valois, and S D Elfar

=====
We measured the spatial-frequency tuning of cells at regular intervals along
tangential probes through the monkey striate cortex and correlated the
recording sites with the cortical cytochrome oxidase (CytOx) patterns to
address three questions with regard to the cortical spatial-frequency
organization. (i) Is there a periodic anatomical arrangement of cells tuned
to different spatial-frequency ranges? We found there is, because the
spatial-frequency tuning of cells along tangential probes changed
systematically, varying from a low frequency to a middle range to high
frequencies and back again repeatedly over distances of about 0.6-0.7 mm.
(ii) Are there just two populations of cells, low-frequency and
high-frequency units, at a given eccentricity (perhaps corresponding to the
magno- and parvocellular geniculate pathways) or is there a continuum of
spatial-frequency peaks? We found a continuum of peak tuning. Most cells
are tuned to intermediate spatial frequencies and form a unimodal rather
than a bimodal distribution of cell peaks. Furthermore, the cells with
different peak frequencies were found to be continuously and smoothly
distributed across a module. (iii) What is the relation between the
physiological spatial-frequency organization and the regions of high CytOx
concentration ("blobs")? We found a systematic correlation between the
topographical variation in spatial-frequency tuning and the modular CytOx
pattern, which also varied continuously in density. Low-frequency cells are
at the center of the blobs, and cells tuned to increasingly higher spatial
frequencies are at increasing radial distances.
=====

And now for something a little more recent:

Cortical Maps of Separable Tuning Properties Predict Population
Responses to Complex Visual Stimuli
Tanya I. Baker and Naoum P. Issa
J Neurophysiol 94: 775-787, 2005.

=====
....

There have been differing descriptions of the organization of spatial
frequency preference in cat Area 17 (Everson et al. 1998; Hubener et al.
1997; Issa et al. 2000; Shoham et al. 1997; Tolhurst and Thompson 1982;
Tootell et al. 1981), but all share the common finding that spatial
frequency preference varies systematically within the space of a
hypercolumn.

....

Previous mappings of the primary visual cortex have shown the existence of
functional domains selective for features of the local spatial Fourier
transform of a stimulus, namely orientation and spatial frequency. However,
the experiments of Basole et al. (2003) showed that these two spatial
variables are not enough to describe distributed cortical responses to
moving images. We showed that the combined organization of spatial and
temporal tuning properties in ferret can account for distributed population
responses to both grating stimuli and more complex stimuli such as drifting
bar textures. This result is consistent with the preliminary report of
Mante and Carandini (2003, 2004). We also used the spatio-temporal
filtering model to make predictions about activity patterns in cat Area 17,
in which spatial and temporal tuning properties are distributed differently
than in ferret V1.
=====

http://jn.physiology.org/cgi/content/full/94/1/775




http://webvision.med.utah.edu/ -->

http://webvision.med.utah.edu/VisualCortex.html -->

http://webvision.med.utah.edu/VisualCortex.html#columns
==============
Orientation and Direction Selectivity.

V1 is the first site where strong orientation and direction
selectivities are observed in the macaque monkey (Hubel and Wiesel,
1968). While the vast majority of V1 cells show some degree of
orientation selectivity, only approximately 25-35% of V1 cells are
strongly directionally selective (Schiller et. al., 1976; DeValois et
al., 1982). The classic method for testing orientation and direction
selectivity is to measure the spike rate of a single cell in response
to drifting oriented luminance bars and/or drifting luminance spots
(see Figure 21).



Figure 21. A tuning curve and corresponding polar plot obtained from
two macaque V1 cells in response to drifting luminance bars of
systematically varied orientation and direction. The responses of one
orientation selective cell and one nonselective cell are provided for
comparison. Histograms surrounding the polar plots demonstrate the
cellular response as a function of time. Orientation bias (OB) and
direction bias (DB) are measures of how selective a cell is, where
0.1 is significant, and 0.3 is approximately an 8:1 maximum firing
rate to minimum firing rate ratio. From Schmolesky et al. (2000). (27K
jpeg image).

The concept of an orientation column can be easily appreciated by
examining figures 20 and 21. When an electrode is lowered into V1 at
an angle relatively parallel to the cortical layers (see Fig. 22) the
orientation selectivities of the cells encountered vary
systematically, where adjacent cellular regions share approximate
orientation preferences.



Figure 22. One extensive electrode penetration in macaque V1. The
short, near vertical lines represent recording sites, and polar plots
for each site are indicated. This figure shows the preferred
orientation of each cell in relation to the cortical layers, CO
compartments (a filled circle indicates a blob; lack of this circle
indicates an interblob) and color selectivity (C=color selective;
B=broadband) in macaque V1. From Leventhal et al. (1995). (27 K jpeg
image)

Such recordings led Hubel and Wiesel to propose models of functional
organization like the one shown below (Figure 23).



Figure 23. The ice-cube model of the cortex. It illustrates how the
cortex is divided, and the same time, into two kinds of slabs, one set
of ocular dominance (left and right) and one set for orientation. The
model should not be taken literally: Neither set is as regular as
this, and the orientation slabs especially are far from parallel or
straight. (27 K jpeg image)

Recently, the orientation columns of V1 first described by Hubel and
Wiesel have also been recast into more complex geometries such as
partial columns ("slabs") and pinwheels as dictated by the increasing
volumes of evidence (e.g. Bonhoeffer and Grinvald, 1991).
====================

.

Relevant Pages

  • Re: Reply to Wolf
    ... probably thinking of the so called "simple cells" of the primary visual ... Orientation and Direction Selectivity. ... selectivity is to measure the spike rate of a single cell in response ...
    (comp.ai.philosophy)
  • Re: Reply to Wolf
    ... V1 may be doing a local spatial frequency analysis of input images is ... I did not claim that the notion that so-called simple cells in V1 can be ... analyzers any more than orientation selectivity makes them "edge detectors" ...
    (comp.ai.philosophy)
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