Utility of the Cortical Evoked Response as a Measure of Photographic Image Quality.

Abstract : This report covers the results of investigation by AMRL into the use of Cortical-Evoke Potentials to measure Photographic Image Quality. This work was sponsored by the Avionics Laboratory using Laboratory Director's Funds. Cortical Evoked Response (ER) procedures (both steady-state and transient) were tested for their utility and sensitivity in indexing the focus level of various kinds of targets. Four studies investigated the ERs generated by presentation of Air Force tri-bar photographs, checkerboard patterns, and complex real imagery. Neither low nor high frequency steady-state ER amplitudes showed sensitivity to defocusing of any type of imagery, although contrast ration clearly produced differences. The phase delay of the fundamental steady-state ER changed significantly with focus of a single tri-bar target. Transient evoked responses showed systematic changes in amplitude as a function of focus. A negative going peak between 90 and 170 msec. after the stimulus appeared to diminish in amplitude with increasingly poorer focus of both checkerboard and complex imagery. Results indicate that, under conditions tested, the steady-state ER does not appear to be a promising technique for assessing image focus, while the transient ER seems considerably more reliable and valid.