The ubiquity and widespread use of digital and online technologies have transformed mental health support, with online mental health communities (OMHCs) providing safe spaces for peer support. More recently, generative AI and large language models (LLMs) have introduced new possibilities for scalable, around-the-clock mental health assistance that could potentially augment and supplement the capabilities of OMHCs. Although genAI shows promise in delivering immediate and personalized responses, its effectiveness in replicating the nuanced, experience-based support of human peers remains an open question. In this study, we harnessed 24,114 posts and 138,758 online community (OC) responses from 55 OMHCs on Reddit. We prompted several state-of-the-art LLMs (GPT-4-Turbo, Llama-3, and Mistral-7B) with these posts, and compared their responses to human-written (OC) responses based on a variety of linguistic measures across psycholinguistics and lexico-semantics. Our findings revealed that AI responses are more verbose, readable, and analytically structured, but lack linguistic diversity and personal narratives inherent in human--human interactions. Through a qualitative examination, we found validation as well as complementary insights into the nature of AI responses, such as its neutral stance and the absence of seeking back-and-forth clarifications. We discuss the ethical and practical implications of integrating generative AI into OMHCs, advocating for frameworks that balance AI's scalability and timeliness with the irreplaceable authenticity, social interactiveness, and expertise of human connections that form the ethos of online support communities.

翻译：数字技术与在线技术的普及及其广泛应用已深刻变革了心理健康支持模式，其中在线心理健康社区为用户提供了安全的同伴支持空间。近期，生成式人工智能与大语言模型的发展带来了可扩展、全天候心理健康援助的新可能，有望增强并补充在线心理健康社区的功能。尽管生成式AI在提供即时个性化回应方面展现出潜力，但其能否复现人类同伴基于经验的支持中蕴含的细腻特性，仍是一个悬而未决的问题。本研究采集了Reddit平台上55个在线心理健康社区的24,114篇帖文及138,758条社区回复，利用多款前沿大语言模型对上述帖文生成回复，并从心理语言学与词汇语义学维度，将其与人类撰写的社区回复进行语言特征对比。研究发现：AI回复虽更具冗长性、可读性与分析性结构，但缺乏人际互动中固有的语言多样性及个人叙事。通过定性分析，我们验证了AI回复的特性并获致补充性洞见，例如其立场中立且缺乏双向澄清的交互行为。最后，我们从伦理与实践层面探讨了将生成式AI整合至在线心理健康社区的问题，倡导建立兼顾AI的可扩展性与即时性、同时保留人类连接中不可替代的真实性、社交互动性与专业性的框架，这正是在线支持社区的精神内核。