There are numerous perceptual illusions relevant to flying - with which one, in particular, are you concerned, here ?

Jukzizy
I don't know what study material you are using. It would help if you could be more specific with your questions. Give a page/question number. This forum cannot help with questions like "I can't understand illusions". You need a book to answer that.

Bob

I'm using bob tait book human performance and limitaion..page 45 about the Terrain sloping up from the threshold/Terrain sloping down from the threahold etc...

I guess the main problem is that the text book words and pictures can't provide the benefit of real life, actual perceptual exposure. Do believe me that the pictures and description just don't cut the mustard.

For instance, I recall - very clearly - my first exposure to rapid fog's developing on the runway (at BK), probably 50 or so years ago, now, The cognitive deficiency in that situation can see the aircraft land short of the runway. This, in total ignorance, I duly did and frightened the daylights out of myself !! In later years, landing in fog in jets was quite routine and presented little problem - certainly helps to know about illusions and the techniques to avoid falling into the traps.

As another anecdote, I landed a B737 at MNG for an airshow fly-in many years ago, severe clear CAVOK conditions - got myself caught out by the illusion associated with a different than familiar runway width - late round out, hard landing, much embarrassment. Really embarrassing for a chap who routinely had greasers on the 73.

Another one which can provide frights, and often fatalities, is the black hole illusion with night landings remote from extensive ground lighting

Some words of wisdom from those who know - https://www.pprune.org/pacific-general-aviation-questions/339634-black-hole-approaches-without-visual-glide-slope-guidance.html

Short of having a look yourself, try a video or two -

https://www.youtube.com/watch?v=3xSlpz0gPCw Horn Island - pretty remote from just about anything. The VASIS is worth its weight in gold.

https://www.youtube.com/watch?v=V96NHi-J2Ao&feature=related night spraying - you just have to be kidding !

https://www.youtube.com/watch?v=vZQ9pS1b4R4 night carrier landings have to count in the most difficult of piloting working activities.

You need to be very aware of the somatogravic illusion before you go off to remote areas by yourself. This one has left broken aeroplanes and bodies around many aerodromes for the past 100 years or so.

For general reading -

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/spatiald_visillus.pdf
https://www.nordian.net/REPOSITORY/108_easa_human_performance_demo.pdf