 Note that, just as observed in rabbit illusion experiments, the formula shows that "l*" underestimates "l" to a greater extent when "t" is made smaller; as "t" becomes large, "l*" approaches "l" and the illusion disappears.The model's parameter, tau (τ), is a time constant for tactile space perception; the value of tau determines how rapidly the perceived length approaches the actual length as the time between stimuli, "t", is increased.The perceived length equals one-third the actual length when "t=τ", and two-thirds the actual length when "t=2τ".