TL;DR: The title says it all. Both are a form of distributed practice. Like a flashcard, the reading material is spaced with an expanding interval. It’s this spaced reading schedule that makes Incremental Reading so special and effective.
You may consider this a complementary article for SuperMemo’s Incremental Reading: Explained.
First, some keywords (source: Improving Students’ Learning With Effective Learning Techniques with slight modification):
Distributed practice refers to distributing learning over time; or in one phrase: spacing your learning.
Distributed-practice effect refers to the finding that distributing practice typically benefits long-term retention more than massed practice.
Interleaved practice: alternating practice of different kinds of items or problems.
Spacing effect: the advantage of spaced over massed practice.
Lag effect: the advantage of spacing with longer lags over shorter lags.
What is the common denominator between SuperNemo/Anki and Incremental Reading?
You probably know that Spaced Repetition Software (SRS) “works” because you need to “recall the information over time”. Two major underlying mechanisms are retrieval practice (recalling information) and distributed practice (spacing across time); or in one phrase: spaced retrieval practice. What you might not realize is that distributed practice (spacing effect) also applies to the reading materials. It’s worth mentioning that distributed practice only means the schedule itself, not what you do during that schedule:
Distributed practice + retrieval practice = SuperMemo/Anki (recall an answer 5 days later)
Distributed practice + reading = Incremental Reading (continue reading 5 days later)
In other words, the spacing effect works on flashcards as well as on reading. Spacing your flashcard review is important, but so is spacing your schedule for reading. This is where Incremental Reading comes in. As I’ve written here, Incremental Reading is about:
I. Reading the source material from start to finish in a spaced manner (distributed practice)
II. Re-reading extracts (highlighted materials) in a spaced manner (distributed practice)
IV: Repeat the above steps for different materials (interleaved practice)
I & III: Distributed practice encompasses the spacing effect and lag effect.
II: Reading more than once is better than reading only once.
Source: The forgetting curve
Two secret sauces behind any Spaced Repetition Software: distributed practice (spacing effect) and retrieval practice (active recall)
The secret sauce behind SuperMemo’s Incremental Reading: distributed practice (spacing effect)
As you can see, distributed practice is the common denominator among SuperMemo/Anki and Incremental Reading.
For the sake of understanding, let’s separate reading and remembering. (P.S.: Massed practice = Cramming; Spaced = Distributed practice)
Cramming in reading: Reading an article, a book chapter, a research paper from start to finish in one setting, e.g, an hour or a day
Spacing in reading: Incremental Reading, spacing your reading across days, weeks or months
Cramming in remembering: Pulling an all-nighter before an exam
Spacing in remembering: Using Spaced Repetition Software (SRS) to space your reviews across days, weeks or months
The secret to reading (learning): Incremental Reading
The secret to remembering: Spaced Repetition Software (SuperMemo/Anki)
I believe Incremental Reading is the other missing half in your journey to knowledge (or studying).