SOLUTION:
public void previous(View view) {
Animation in = AnimationUtils.loadAnimation(this, android.R.anim.slide_out_right);
Animation out = AnimationUtils.loadAnimation(this, android.R.anim.slide_in_left);
imageSwitcher.setInAnimation(out);
imageSwitcher.setOutAnimation(in);
Uri imageUri = Uri.parse(imageDir+"/"+imageNames[i]);
imageSwitcher.setImageURI(null); // THIS FIXED THE OOM ERROR
imageSwitcher.setImageURI(imageUri);
decrementImage();
}