When Herrnstein (1961) gave pigeons and rats a choice between a response alternative that offered food reinforcers according to a VI 90-second schedule and another alternative that never paid off...

Herrnstein was surprised when the animals simply stopped responding.

Herrnstein was surprised when the animals exclusively preferred the alternative that never paid off.

Herrnstein was surprised when the animals allocated their behavior equally between these alternatives.

Herrnstein was not all surprised when the animals exclusively preferred the VI 90-second alternative.