Subject: Human vision in the near-infrared realm

I have been told that the human eye, under a condition of altered atomic
state of certain vision-related retinal substances, presents a visual 
capability under near-infrared "light". That is, under such a condition, 
the human eye will see objects that are illuminated by, or that emit 
near-infrared "light".

Is that really true ?

If so, how does it work ? What causes it ? 

Is that a normal, or an abnormal eye condition ?

Under such a condition, which would be the near-infrared band width 
perceived as visible light by such an human eye ?

On the practical side, what can be expected from this ? 

Re: Human vision in the near-infrared realm