2.5. Experiment 1-4: Hemispheric Asymmetry of Non-Color Detection in Rightand Left-Handed Individuals

2.5.1. Purpose

This experiment was designed to identify the critical factor for the asymmetry observed in Experiment 1-2. We determined whether the asymmetry observed in the detection of color might also be found in the detection of achromatic stimuli or not. If the asymmetry was lost using achromatic stimuli, it should therefore be ascribed to color processing and not to other factors.

2.5.2. Methods

2.5.2.1. Participants

Twelve right-handed (6 males and 6 females, mean age 20.5 years, SD 2.8) and eight lefthanded undergraduate students participated in the present experiment. Six right-handed subjects were the same individuals who participated in Experiment 1-1, while the other six subjects were those who participated in Experiment 1-2. All left-handed subjects were those who participated in Experiment 1-3.

2.5.2.2. Apparatus

An achromatic solid circle with a diameter of 2 deg (x = 0.283, y = 0.320, CIE) was presented on the CRT with a uniform gray background of 10 cd/m2 (Fig. 11). In the six righthanded participants who participated in Experiment 1-1, luminance of either 12, 14, or 18 cd/m2 was tested, while in other six right-handed participants who participated in Experiment 1-2, as well as in the eight left-handed participants, only a luminance of 20 cd/m2 was used.

Figure 11. Schematic illustration of the time schedule for Experiment 1-4. A trial started with an auditory ready signal preceding 1-4 sec with a mean of 2.5 sec. A target was presented at 4 deg lateral to the fixation point. either left or right visual field for 0.5 sec. A total of 15 trials were performed with an intertrial interval of 10-20 sec with a mean of 15 sec. The target was an achromatic circle with a diameter of 2 deg, either 12, 14, 18 or 20 cd/m2 with a gray background of 10 cd/m2.