Class of words including Gehörtes, Gesehenes, Gesprochenes

Question

I recently came across the following sentence:

Gehörtes oder Gelesenes kann man mit der direkten oder der indirekten Rede wiedergeben.

The words Gehörtes and Gelesenes were new to me and after further searchs on Linguee.com it seems that there is a set of similar words including Gesehenes, Gesprochenes, Erlebtes, Gelesenes (potentially more) with the following characteristics:

1. Take the role of a noun in a sentence
2. Have the sense of “what is seen, heard, read etc”
3. Formed with the past participle of a verb + “es”
4. Do not have the definitive article and do not decline

Do I have this correct?

Also, the form and usage seems quite productive and I would like to know what set of verbs can be included.

Answer 1

You found out about the so called Nominalisierung:

Nominalisierung means: In German you can build a noun from about every verb by just adding an article and writing it with a capital letter:

Ich schwimme - das Schwimmen

Du fährst - das Fahren

Er singt - das Singen

If you take the verb in its participle 2 Form, then it stands for the object of the action. This does not work with all verbs, but with many of them. The first step is usually to use the participle as an adjective to a noun, then the second step is to omit the noun:

Er singt ein Lied — das gesungene Lied ist schön

• das Gesungene ist schön

Ich höre Die Worte

• die gehörten Worte gefallen mir
• das Gehörte gefällt mir

As you see: these participle nouns are always neuter (using das), independant of the omitted word.

And: you can even omit the article, then it is nothing specific but more generic:

Gelesenes kann man sich besser merken als Gehörtes

Here you do not reference something specific that you heard or read, but speek about general thing you hear verses general things you read.

You can read some more basics about this in this German article at Pons.