  Recall impairment in a different environmental context from learning is
called context-dependent forgetting. Two learning methods have been proposed to
prevent context-dependent forgetting: reinstatement and decontextualization.
Reinstatement matches the environmental context between learning and retrieval,
whereas decontextualization involves repeated learning in various environmental
contexts and eliminates the context dependency of memory. Conventionally, these
methods have been validated by switching between physical rooms. However, in
this study, we use immersive virtual environments (IVEs) as the environmental
context assisted by virtual reality (VR), which is known for its low cost and
high reproducibility compared to traditional manipulation. Whereas most
existing studies using VR have failed to reveal the reinstatement effect, we
test its occurrence using a 360-degree video-based IVE with improved
familiarity and realism instead of a computer graphics-based IVE. Furthermore,
we are the first to address decontextualization using VR. Our experiment showed
that repeated learning in the same constant IVE as retrieval did not
significantly reduce forgetting compared to repeated learning in different
constant IVEs. Conversely, repeated learning in various IVEs significantly
reduced forgetting than repeated learning in constant IVEs. These findings
contribute to the design of IVEs for VR-based applications, particularly in
educational settings.
