Quick Optical Sensor Question

[zorro]

I was playing around with an optical sensor today and am curious why they require two digital inputs. When I hooked one up today and observed its behavior, I noticed that when a reflection was detected the two values of the inputs were swapped (the 1 became a 0 and the 0 became a 1). I could not get only one value to change at a time nor both the values to become equal. It seems to me that the use of two sensor inputs is a waste if this is the case. Can anybody confirm that this behavior is what is expected? If not, could you please explain how to elicit a different reaction?

Thanks in advance,
Greg Szorc