RESULTS 

[1] Comparison of peak latencies between congenitally blind subjects and those with normal vision showed a significant difference (two factor ANOVA) between the Nb wave peak latency (38 ms-48 ms range) of the two groups, viz., congenitally blind and normal sighted [F for Factor A = 5.35, since F.05 (1) 1,36 = 4.1 1, hence p < .05 ]. However, there was no significant difference between the repeat assessments, i.e., RI and R2, Factor B (p > .50), and the interaction between factors (A x B) was also not significant (p > .10). The F value for df = 1.36 has been derived by linear interpolation from the df = 1.30 and df = 1.40 from the standard table as has been described (Zar. 1984). 

Also, the Tukey test for multiple comparisons between mean values showed a marginal significant difference between the mean values (second assessments) of the congenitally blind and normal sighted subjects [q = 3.65, since q at probability level .07 for df = 36, 4 = 3.62, hence p < .07]. The significantly lower Nb wave peak latency in the congenitally blind group was observed as: (1) a difference of more than 3.0 ms in 4 subjects, (2) more than 1.0 ms in 2 subjects, (3) in 3 subjects this difference was less marked (0.56 to 0.83 ms) and (4) in a single CB subject the Nb wave peak latency was higher (by 1.0 ms). Two examples of (1) and a single example of (3) are illustrated in Figure 1. The two factor ANOVA did not show significant differences between either factors or interactions for the peak latencies of the other AEP-MLRs component (p< .20, in all cases).

 [2] Comparison of the peak amplitudes of the Pa and Nb waves recorded from the occipital area (Oz) showed that the peak amplitude of the Pa wave at Oz was significantly lower in the congenitally blind compared to the normal vision group [F for Factor A= 5.07, since F.05 (1) 1,36 = 4.11, hence p <.05]. There was no significant difference between repeat assessments or interaction between factors (Factors B, A x B, p > .20) for Pa wave. For the Nb wave there were also no sig- nificant differences (Factor A, Factor B, A x B, p > .50). 

When recordings were made at Cz, there were no significant differences for all 4 auditory evoked potential components studied (p > .20, for all comparisons).

FIGURE 1:  Three examples of AEP-MLRs recorded in three pairs of congenitally bling(CB) and normal vision(NV) subjects. The first two pairs (I,II) shows examples of noticeabley lower Nb wave peak latency in CB group subjects compared to NV group subjects. The third pair (III) shows a less obvious difference in Nb wave peak latency between the two groups.

The group average values of peak amplitudes and latencies of the four components studied. for the congenitally blind and normal sighted subjects are given in Table 1.

TABLE 1: Peak latencies and peak ainplitudes of AEP-MLRs recorded in congenitally blind (CB) and normal vision (NV) subjects, (N = 1 0)