Query Expansion and Key Specialization in Transformer Attention Geometry
This study investigates the divergent geometric evolution of query (Q) and key (K) projections during Transformer training and its implications for the attention mechanism. By systematically monitoring the training trajectories of small GPT models through participation ratio analysis, effective dimensionality tracking, and spectral control experiments, this work reveals, for the first time, the dynamic evolution of Q/K geometric asymmetry: the effective dimensionality of Q expands while that of K contracts. Furthermore, it establishes a causal link between this asymmetry and changes in attention entropy. Experimental results confirm that spectral contraction in K directly drives the sharpening of attention distributions. The findings also characterize the universality of these geometric trends during early training and their subsequent decay in later stages, offering a novel perspective for understanding attention mechanisms.