Latent Positional Information is in the Self-Attention Variance of Transformer Language Models Without Positional Embeddings

Ta-Chung Chi, Ting-Han Fan, Li-Wei Chen, alexander rudnicky, Peter J Ramadge

Main: Large Language Models Main-poster Paper

Poster Session 2: Large Language Models (Poster)
Conference Room: Frontenac Ballroom and Queen's Quay
Conference Time: July 10, 14:00-15:30 (EDT) (America/Toronto)
Global Time: July 10, Poster Session 2 (18:00-19:30 UTC)
Keywords: interpretability/analysis
TLDR: The use of positional embeddings in transformer language models is widely accepted. However, recent research has called into question the necessity of such embeddings. We further extend this inquiry by demonstrating that a randomly initialized and frozen transformer language model, devoid of positio...
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Abstract: The use of positional embeddings in transformer language models is widely accepted. However, recent research has called into question the necessity of such embeddings. We further extend this inquiry by demonstrating that a randomly initialized and frozen transformer language model, devoid of positional embeddings, inherently encodes strong positional information through the shrinkage of self-attention variance. To quantify this variance, we derive the underlying distribution of each step within a transformer layer. Through empirical validation using a fully pretrained model, we show that the variance shrinkage effect still persists after extensive gradient updates. Our findings serve to justify the decision to discard positional embeddings and thus facilitate more efficient pretraining of transformer language models.