If page is attachment, THEN run this code

add_filter('wpseo_title', 'my_seo');
function my_seo($title) {
	$title = str_replace('-', ' ', $title);
	return $title;
}

I wrote that little code but I want it to affect ONLY attachment pages, I run a gallery site so a lot of my images have – which Id rather replace with blank space. But when I run this code, it changes for all pages on my site, I want this code to only activate on the attachment pages.

I know I have to use an IF statement(right?) but I am, stuck there, please assist.