New paper in Schiz­o­phre­nia Bul­letin Open: Erb et al., Aber­rant per­cep­tu­al judge­ments on speech-rel­e­vant acoustic fea­tures in hal­lu­ci­na­tion-prone indi­vid­u­als

Hal­lu­ci­na­tions – per­cepts in the absence of an exter­nal stim­u­lus – con­sti­tute an intrigu­ing mod­el of how per­cepts are gen­er­at­ed and how per­cep­tion can fail. They can occur in psy­chot­ic dis­or­ders, but also in the gen­er­al pop­u­la­tion.
Healthy adults vary­ing in their pre­dis­po­si­tion to hal­lu­ci­na­tions were asked to iden­ti­fy “speech” in ambigu­ous sounds. Lis­ten­ers qual­i­fy­ing as more hal­lu­ci­na­tion-prone in two estab­lished ques­tion­naires per­cep­tu­al­ly down-weight­ed the speech-typ­i­cal low fre­quen­cies (pur­ple sub­group in the fig­ure for illus­tra­tion). Instead, the hal­lu­ci­na­tion-prone indi­vid­u­als pri­ori­tised high fre­quen­cies in their “speech­i­ness” judge­ments of ambigu­ous sounds.
At the same time, the high­er one scored on hal­lu­ci­na­tion-prone­ness, the more con­fi­dent on a giv­en (always ambigu­ous!) tri­al they were. Hal­lu­ci­na­tion-prone­ness and actu­al sen­so­ry evi­dence had a com­pa­ra­ble impact on con­fi­dence, con­sis­tent with the idea that the emer­gence of hal­lu­ci­na­tions is root­ed in an altered per­cep­tion of sounds.
This research may con­tribute to improv­ing ear­ly diag­no­sis and pre­ven­tion strate­gies in
indi­vid­u­als at risk for psy­chosis.

From the abstract:
“Hal­lu­ci­na­tions con­sti­tute an intrigu­ing mod­el of how per­cepts are gen­er­at­ed and how per­cep­tion can fail. Here, we inves­ti­gate the hypoth­e­sis that an altered per­cep­tu­al weight­ing of the spec­tro-tem­po­ral mod­u­la­tions that char­ac­ter­ize speech con­tributes to the emer­gence of audi­to­ry ver­bal hal­lu­ci­na­tions. Healthy adults (N=168) vary­ing in their pre­dis­po­si­tion for hal­lu­ci­na­tions had to choose the ‘more speech-like’ of two pre­sent­ed ambigu­ous sound tex­tures and give a con­fi­dence judge­ment. Using psy­chophys­i­cal reverse cor­re­la­tion, we quan­ti­fied the con­tri­bu­tion of dif­fer­ent acoustic fea­tures to a listener’s per­cep­tu­al deci­sions. High­er hal­lu­ci­na­tion prone­ness covar­ied with per­cep­tu­al down-weight­ing of speech-typ­i­cal, low-fre­quen­cy acoustic ener­gy while pri­ori­tis­ing high fre­quen­cies. Remark­ably, high­er con­fi­dence judge­ments in sin­gle tri­als depend­ed not only on acoustic evi­dence but also on an individual’s hal­lu­ci­na­tion prone­ness and schizo­typy score. In line with an account of altered per­cep­tu­al pri­ors and dif­fer­en­tial weight­ing of sen­so­ry evi­dence, these results show that hal­lu­ci­na­tion-prone indi­vid­u­als exhib­it qual­i­ta­tive and quan­ti­ta­tive changes in their per­cep­tion of the mod­u­la­tions typ­i­cal for speech.”
The paper is avail­able here.