\documentclass[12pt]{letter}
\usepackage {fullpage}
\usepackage {palatino}
\pagestyle{empty}
%\def\setstretch#1{\renewcommand{\baselinestretch}{#1}}
%\setstretch{1.1}
%\setlength{\topmargin}{-0.4in}
%\setlength{\textheight}{9.8in}
%\setlength{\textwidth}{6.2in}
 
\begin{document}

\signature{
Rich Zemel
}

\begin{letter}

Dr. David A. Rosenbaum\\
Department of Psychology\\      
Pennsylvania State University\\
642 Moore Building\\
University Park, PA \ 16802-3104

\vspace{.5in}

We would like to submit a revised version of our manuscript, entitled 
``Experience-Dependent Perceptual Grouping and Object-Based Attention'', for 
consideration for publication in the {\it Journal of Experimental Psychology:
 Human Perception and Performance}.

\vspace{.1in}

We have carefully considered the comments, criticisms, and suggestions of all
three reviewers.  The resulting manuscript has been significantly 
modified, particularly with respect to the statistical analyses, and
to the general discussion, mainly in reference to earlier work.  We
address the comments of each reviewer in turn:

\vspace{.3in}

{\bf Reviewer A}

One main criticism that this reviewer had concerned the placement of
our work in the context of previous work.  In particular, the reviewer
thought that the work of Chen and Baylis and Driver showing that explicit
instructions affect parsing was given short shrift.  We do not think that
in any way was this work included as an after-thought -- it was discussed in
the first main sub-section of the General Discussion.  We have expanded
this discussion, and have includec the reviewer's excellent suggestion that
our work can be considered as an extension of this earlier work if one views
perceptual experience as a form of implicit instruction about how to
parse an image.

A second criticism was that the main issues in the paper should have been
framed as a contrast between bottom-up and top-down influences rather than 
between generic grouping principles and perceptual experience.	Our view
is that the terms ``bottom-up'' and ``top-down'' have different meanings
to different groups, in different contexts.  Domain knowledge, such as
familiar relations between image features, can easily be integrated into
``bottom-up'' connections in a neural network.  This is what MAGIC does.
So the same effect, such as the experiments in this paper, can be viewed as
either bottom-up or top-down depending on one's theoretical perspective and 
interpretation of the terms.  We have added a paragraph discussing this
point to the General Discussion.

A third criticism concerned the size of the manipulation in the final
experiment.  As Reviewer C noted, these manipulations appear small,
but are fairly sizable when considered in the context of the highly
position-specific effects found in perceptual learning experiments.
A sentence noting this was added to the manuscript.
In addition, we clarified that this experiment was not addressing
general viewpoint-specificity, but rather a more constrained
form of specificity with respect to absolute position.

A fourth criticism concerned the discussion of previous accounts of
object-based attention.
We agree that this discussion was muddled in the original manuscript.  The
main issue was not models of object-based attention, but rather the
interaction between object- and space-based attention.  We have attempted to
clarify the discussion.

Minor comments have been addressed as well: we added bump line length
information; included the idea of using multiple alternative objects
within single experiment in the future work section;
clarified wording concerning object effects across blocks; re-labeled the
groups in Experiment 1; and included a discussion of the more significant
difference for feature location on the Small-Ends versus Large-Ends
displays in the final experiment.
We also fixed the Vecera \& Farah (1994) citations -- these were
meant to be Vecera (1994).

\vspace{.3in}

{\bf Reviewer B}

This reviewer found that the main weakness of the paper was that it did
not quantify the relative influence of Gestalt principles versus recent
experience in determining perceptual organization.  We agree that this
is a critical issue that our paper does not address.  Our only answer
at this point was to include a discussion of this point in the future
work section.

A second criticism of this reviewer concerned the MAGIC model.  The
reviewer is entirely correct that our findings do not validate this model,
and that this model is not the only model that can account for the
data.  We added a paragraph to this effect in the General Discussion.

A third point made by this reviewer concerns historical context for the
work.  We've adopted the suggestion that this work be placed in the
context of the debate between the Brunswick versus Gestalt schools.

\vspace{.3in}

{\bf Reviewer C}

The reviewer had numerous suggestions about the statistical analysis.
In some cases, we only reported on some of the results in order to
highlight what we consider the main effects; in other cases, we
unintentionally omitted some results.  In the new version, we have 
reported on the full set of ANOVAs, and have also run some new ANOVAs 
on the old data, following the reviewer's suggestions.  For all
experiments, error analyses are included along with reaction times.
Results of an ANOVA crossing all the main experimental factors, including
judgement and orientation, are reported first, followed by separate
analyses on separate blocks or groups.  Hence the results sections are a
bit denser but more thorough and complete.

The reviewer suggested that previous work by Nakayama and colleagues,
particularly Joseph and Nakayama (1999) be cited and discussed.  We
have added these to the General Discussion.
We have also included sentences discussing Wertheimer's suggested role for
experience in grouping, and Gauthier and Tarr's proposal that object
representations may be fuzzy with respect to shape.

All of the more minor comments of this reviewer have been addressed as
well, including several rewordings, typos, and figure modifications.

\vspace{.5in}

We hope that this answers the comments and objections of the reviewers
and look forward to hearing from you.

\vspace{.3in}

\begin{tabbing}
\hspace{3.in}\= Thanks and best regards, \\[.8in]
\> Richard Zemel\\
\> Department of Computer Science\\
\> University of Toronto\\
\> Toronto, ON  ~ M5S 1A4 ~ Canada\\
\> phone: 416-978-7497\\
\> fax: 416-978-1455\\
\> email: zemel@cs.toronto.edu
\end{tabbing}

\end{letter}
\end{document}

