It depends on the person. Some have visual images of themselves, others connect to feelings or perceptions. And for others, nothing happens during a regression and later it comes to them in floods or in brief revelations. But it is never about accuracy. It is more about an impression. Regression may not be accurate but it can be very useful.
For example, I once regressed an argumentative and hostile woman, who plagued those around her with her miserable temper and antagonism. Her employer asked me to regress her, out of desperation. She dropped into a deep trance, snoring. I thought I had lost her to sleep. Yet, when she came out of the regression she told me of many images that appeared to her of when she had been an abused slave in various countries.
She understood that she had been carrying these hidden memories in her subconscious. Once she saw them, she was able to understand her nasty ways and knew she was dragging past life misery into this life. She jumped up, hugged me with great joy, smiled continuously and ended up changing the way she treated people from that day on.
Her life changed. She attracted a mate and got married, had friends, treated people kindly, and was all around a happier person. So this is not proof of reincarnation but it is an effective way for people to understand themselves better and to uncover underlying issues. I have seen it many times. The joy of understanding that we are Eternal Souls paying a visit in the physical form is liberating. It can be attained through a good past life regression session.