Evaluation of auditory spectral resolution, speech understanding in noise and verbal language skills in individuals with intellectual disability

In this study, it was aimed to evaluate the auditory spectral resolution skills, speech comprehension in noise, verbal memory processes and verbal language skills of individuals with mild intellectual disability (MID) and to analyze the variables relationally. The study included 27 individuals diagnosed with ADHD and 27 typically developing individuals. Audiologic evaluations, Hearing in Noise Test (HINT-PV), Verbal Memory Processes Test (VMPT) and Spectral Modulation Ripple Test (SMRT) were performed in all participants. The Turkish School Age Language Development Test (TODIL) test was administered to individuals diagnosed with MID. While the threshold levels of all participants with normal hearing were similar between the groups in the HINT quiet condition (p>0.05), differences were observed between the two groups in the HINT noise precondition, SMRT test R/O, SBST-ABP, SBST-TÖP, SBST-EYÖP, SBST-USB tests (p<0.001). It was observed that individuals with HINT obtained lower language scores in verbal language skills than the test norm values (p<0.05). The results of the groups in terms of gender and threshold levels in the HINT-quiet condition were similar (p>0.05). Individuals with SMRS were analyzed in two groups: 15 individuals (55.6%) with intelligence quotient (IQ) 50-59 and 12 individuals (44.4%) with IQ 60-69. A difference was observed between the two subgroups in SMRT R/O, SBST TÖP, EYÖP, USB, TODİL test results with HINT noise precondition (p<0.01). A positive correlation was observed between mental ability level and SMRT-R/O, SBST-TASP, SBST-ESP and SBST-USB in individuals with MID (p<0.05). A positive correlation was observed between the HINT-noise covariate and SMRT-R/O, SMRT-TASP, SMRT-USB and SMRT-ESP in individuals with MID (p<0.05). No significant correlation was observed between the HINT noise covariate and SMRT R/O and HINT silent condition (p>0.05). In conclusion, in our study, it was evaluated that individuals with HINT may have deficiencies in spectral resolution skills at the level of peripheral and central auditory pathways and auditory cortex even if they have normal hearing thresholds. The fact that lower R/O scores were obtained as the level of intellectual disability decreased suggests that intellectual disability is associated with processing and discrimination in auditory cortical areas, and spectral resolution skills seem to be affected. It was observed that individuals with lower levels of intellectual disability achieved lower success in verbal language skills and verbal memory processes, which resulted in lower learning performance, worse performance in the HINT noise precondition, and a need for higher signal to noise ratio (SNR). Likewise, it can be said that their language skills improved with increasing intellectual ability level and they were more successful in speech comprehension skills and verbal memory processes in noise. Individuals with intellectual disabilities seem to need more SNR.