Absence of an Odd-Error Signal Mechanism in Human Accommodation

Experiments have been designed to demonstrate that the human accommodative system operates with an even-error signal mechanism under restricted monocular viewing conditions. Retinal blur is such an even-error input signal and, thus, these experimental results add to the evidence considering blur as the effective input signal in accommodation. The random 50 percent erroneous initial direction of movement is a null experimental result which should be robust to a variety of experimental artifacts that may have contaminated previously published results.