Change the title attribute of <a></a> tag on the category/tmpl/default.php page

[alexmiras]

I want to change code to the product image link on a category page
// Show Products ?>
      <div class="product floatleft<?php echo $Browsecellwidth . $show_vertical_separator ?>">
               <div class="spacer">
            <div class="width30 floatleft center">
               <?php /** @todo make image popup */
                     echo $product->images[0]->displayMediaThumb('class="browseProductImage" border="0" title="'.$product->product_name.'" ',true,'class="modal"');
                  ?>
The title of the <a></a> tag it seems to be hardcoded. It shows the <img/> filename and I would prefer the title="'.$product->product_name.'" my lightbox or tooltip  js take this attribute for content or title and is more meanfull the .$product->product_name. than the image filename
How can I change or overwrite that?
Joomla! 2.5.4 Stable, Virtuemart 2.0.6 and PHP 5.3.8
Sorry