Table 3.

Mean (± SEM) subjective measures for the Stanford Sleepiness Scale (SSS), and measure on the visual analog scales (VAS) for relaxation, alertness, concentration and task difficulty.

	Simple Detection		Arithmetic
	Low Accuracy	High Accuracy	Low Accuracy	High Accuracy
SST	3.52 ± 0.27	3.57 ± 0.33	2.37 ± 0.22	2.71 ± 0.34∧
VAS – relaxation	1.61 ± 0.26	2.58 ± 0.30	3.31 ± 0.48	3.60 ± 0.45∧
VAS – alertness	4.16 ± 0.46	3.89 ± 0.58	6.28 ± 0.51	4.96 ± 0.49∧
VAS – concentration	4.43 ± 0.57	3.89 ± 0.39	3.30 ± 0.42	3.79 ± 0.53
VAS – difficulty	0.80 ± 0.24	2.24 ± 0.54	3.46 ± 0.46	2.63 ± 0.49*

Note. ^∧for a significant main effect of task, * for a significant interaction effect between task and accuracy group.

For VAS 10 cm scales were used. Each end of the scale was labeled as follows.

Relaxation: very relaxed – very stressed.

Alertness: very tired/sleepy – very alert.

Concentration: very easy to concentrate – very difficult to concentrate.

Difficulty: very easy – very difficult.