Detection of visual signals by rats: effects of signal intensity, event rate, and task type

Animal models of human cognitive processes are being developed for investigating the neurobiological mechanisms of these processes and for identifying potential therapies for intoxication and neurodegenerative diseases. One promising method involves assessment of sustained attention in rats by use of a discrete-trial signal detection task. Several psychophysical and procedural factors have been identified in the literature that affect sustained attention in normal human subjects. Three key parameters that affect the level of performance, and whether that performance level deteriorates over time, include the quality of the signal, the event rate, and the type of task employed (simultaneous or successive discrimination). These three parameters were manipulated in this study to assess the degree of similarity in the behavior patterns engendered in rats by this signal detection task, in relation to the behavior observed in humans performing a variety of sustained attention tasks. Signal quality was manipulated by varying the increment in the intensity of a lamp (duration=300 ms), and event rate was varied among values of 4, 7, and 10 trials/min. The 'standard' detection task was used as a simultaneous discrimination and a successive discrimination task was designed in which a dim light flash was defined as a non-signal event and any of three brighter flashes were signal events. Accuracy of signal detection was quantified by the proportion of correct detections of the signal [P(hit)] and the proportion of false alarms [P(fa), i.e., incorrect responses on non-signal trials]. P(hit) fell with decreasing signal intensity, increasing event rate, and was lower in the discrimination task compared to the detection task. P(fa) increased with increasing event rate, but only in the detection task. A decrement in P(hit) across trial blocks was observed in the discrimination task primarily, and was most evident with a high event rate and dim signals. These data confirm that these tasks assess process(es) in rats that are very similar to those considered as sustained attention in humans.