If rats are exposed successively to white noise, then to recorded rat squeals, or alternatively to squeals first and then white noise, and if, in both situations, they are allowed to shut off the auditory stimulation by applying pressure on a bar, they will touch the bar more frequently when exposed to white noise. The results indicate that the bar-pressing behavior is the expression of increased activity resulting from the increased stimulation.

No abstract

Sampson has demonstrated that, for very brief exposure times only, the use of the non-dominant eye, determined by an aiming test, results in poorer performance in a serial addition task. The present study reports that when fixation points are supplied, the differences between the dominant and non-dominant eye, at these very brief exposure times, disappear. Sampson concluded that information from the non-dominant eye is integrated more slo,wly than that from the dominant eye. The present study questions the validity of this conclusion.

Two experiments were carried out to determine the functional relation between the critical flicker frequency (CFF) of two identical intermittent targets, binocularly superimposed, and the phase difference between the targets. Binocular CFF is a monotonic decreasing function of phase difference, positively accelerated for phase differences between 0° and 180", and negatively accelerated for phase differences between 360° and 180°. It is postulated that the results can be accounted for by assuming the existence of something akin to the "isodynamic" cells of Cajal, and that more weight is attached to the input to these cells from one eye than from the other.

Fig. 1. Sc hemati c representation of (he functi onal rel at ion between bar pre ssing and noise le vel. level at or below the ambient noise (62 db) level of the room in which the animals were kept produced a steady rate of 2 to 3 bar presses per session with no increment through 10 days. Therefore, four levels of noise were used in the present experiment with increments of 12 db over the ambient noise level, Le., 74, 86, 98 and 110 db re 0.0002 dyne/cm 2.A total of 20 male rats of the Wistar strain were used, five for each group. Each group was subjected to one noise level. For 28 consecutive days prior to the experiment, each of 20 rats was handled for a 10 min. period each day.During any experimental session the rat was placed in the experimental box and exposed for 10 min. to a selected constant level of white noise. If the r at pressed the bar, the noise was interrupted for 15 sec. Depressions of the bar during a 15 sec. quiet period resulted in additional quiet periods of 15 sec.Each group was tested until its frequency of bar pressing reached a constant value. As a result the 74 and 86 db groups were run for 17 consecutive days, and the 98 and 110 db groups were run for 29 consecutive days. ResultsThe results are shown schematically in Fig AbstractThe experiment shows the rate of bar pressing by the rat as a function offour ambient white noise levels, when a bar press interrupts the noise for 15 sec. The results indicate an inverted U'-shaped relation at the beginning of the experiment. As successive exposures to white noise take place, the relation changes progressively to a linear one. These findings support the sensory reinforcement hypothesis, and are discussed in relation to an a priori distinction between stimulus anddrive. It is suggested that the same state may serve as both. Two theoretical explanati ons can explain these findings. ProblemBarnes & Kish (1957) have shown that when depression of a platform interrupts a white noise, rats exposed to the noise will spend considerably more time on the platform than rats not exposed to it. Similarly, Lavery & Foley (1963) have shown that rats will press a bar to interrupt white noise. Each of these studies used a specific level of white noise. The purpose of the present experiment was to determine the functional relation between noise level and this type of behavior. The study examined the frequency of bar pressing as a function of the ambient level of white noise, when each bar press interrupted the noise for 15 sec. MethodThe experimental box, 11 in wide, 12 in long, and 8.5 in deep, was made from 0.5 in plywood, with a metal grid floor and ceiling. Thehorizontalpartofa T-shaped metal bar, 3.25 in long, and of square cross section 0.25 in on the side, protruded 1 in into the box through the floor 0.75 in from one end wall. The vertical stem of the T-shaped bar was connected outside the box to a microswitch which was operated by gentle pressure against the T-bar. The microswitch was in turn connected to Hunter timers and an Esterline-Angus recorder.T...