Google Scholar is good for searching broadly since it contains content from all disciplines or for performing comprehensive searches since it pulls articles from most journals.
Let's start by going to Google Scholar and entering the search terms "development visual cortical neurons."
Things to note from this example:
Abstracts are freely available for most of the articles. Reading the entire article may require a subscription, but CMU probably has subscriptions to journals you would be interested in using for this class. If you are on campus, you can click directly on the title of the article to get full-text and PDFs on the publisher's website or you can click on the [PDF] links on the right to go directly to a PDF.
Note: If you are off campus, you will usually need to login to the VPN to access full-text and PDFs. Follow the instructions here. Email firstname.lastname@example.org if you are still having issues accessing articles.