Had to look it up
The von Neumann–Wigner interpretation, also described as "consciousness causes collapse", is an interpretation of quantum mechanics in which consciousness is postulated to be necessary for the completion of the process of quantum measurement.
Italics mine, to emphasize that the hypothesis is not accepted in mainstream physics. It is not consciousness but interactions that model the probable outcomes of experiments.
One does not need to set up double slits with observers, as there are an enormous number of data in high energy particle physics that clearly separate measurements in decohered classical space from the basic quantum mechanical interaction.
To get an intuitive understanding, think of bubble chamber pictures:
The quantum mechanical probabilistic interaction happens at the vertices ,the film is the recording with decohered interactions of the charged particles with the hydrogen atoms of the chamber. Thousands upon thousands of pictures are recorded and stored.
The measurement of the quantum mechanical probability distribution comes from scanning and measuring in the geometry on the film, the same type of interaction, in this case the creation of an (omega-) particle, the cherry on the decouplet prediction of the quark model.
These measurements are independent of the interaction, which happened once , when the film was triggered, and there was no consciousness there, just programmed machines. The same probability distribution ( the quantum mechanical interaction)will come up again, if the films are looked over again.
At present the detectors are sophisticated electronic detectors, but the argument is the same: the data are stored by smart electronics, and the same quantum mechanical probabilities will show up every time they are examined.
No conscious observers affecting the interactions, so the hypothesis is disproved .