protected function getDisplayableTypes()
    {
        $displayable_types = array();

        foreach ($this->accept_mime_types as $mime_type) {
            $displayable_type = isset($this->human_file_types[$mime_type])
                ? $this->human_file_types[$mime_type]
                : $mime_type;

            // Use the value as the key to de-dupe.
            $displayable_types[$displayable_type] = $displayable_type;
        }

        return $displayable_types;
    }