This study was examined the effects of trace interval on conditioned response between delayed and trace conditioning. Twenty subjects assigned to delayed conditioning group or trace conditioning group. A pure tone was used as CS, and an electric shock of 5 mA was used as UCS. Duration of CS was 10 seconds, and trace interval was 20 seconds. In delayed conditioning group, CS was immediately followed by UCS at CS-offset. In trace conditioning group, CS was followed by trace interval, and UCS was presented after trace interval. Six reinforcements were administered for subjects of both groups. Phasic changing pattern of HR were measured as indices of CR. The results were as follows : (1) In delayed conditioning group, HR during CS presentation showed triphasic changing pattern, while HR in trace conditioning group showed decelerative changing pattern. (2) Before UCS presentation, HR showed triphasic changing pattern both in delayed and trace conditioning. These results indicated that trace interval would affect CR acquisitive process
