Portrait of Amirhossein Kazemnejad is unavailable

Amirhossein Kazemnejad

Master's Research - McGill University


Measuring the Knowledge Acquisition-Utilization Gap in Pretrained Language Models
Amirhossein Kazemnejad
Mehdi Rezagholizadeh
Prasanna Parthasarathi
The Impact of Positional Encoding on Length Generalization in Transformers
Amirhossein Kazemnejad
Inkit Padhi
Karthikeyan Natesan
K. Ramamurthy
Payel Das
Length generalization, the ability to generalize from small training context sizes to larger ones, is a critical challenge in the developmen… (see more)t of Transformer-based language models. Positional encoding (PE) has been identified as a major factor influencing length generalization, but the exact impact of different PE schemes on extrapolation in downstream tasks remains unclear. In this paper, we conduct a systematic empirical study comparing the length generalization performance of decoder-only Transformers with five different position encoding approaches including Absolute Position Embedding (APE), T5's Relative PE, ALiBi, and Rotary, in addition to Transformers without positional encoding (NoPE). Our evaluation encompasses a battery of reasoning and mathematical tasks. Our findings reveal that the most commonly used positional encoding methods, such as ALiBi, Rotary, and APE, are not well suited for length generalization in downstream tasks. More importantly, NoPE outperforms other explicit positional encoding methods while requiring no additional computation. We theoretically demonstrate that NoPE can represent both absolute and relative PEs, but when trained with SGD, it mostly resembles T5's relative PE attention patterns. Finally, we find that scratchpad is not always helpful to solve length generalization and its format highly impacts the model's performance. Overall, our work suggests that explicit position embeddings are not essential for decoder-only Transformers to generalize well to longer sequences.
The Curious Case of Absolute Position Embeddings
Koustuv Sinha
Amirhossein Kazemnejad
Dieuwke Hupkes
Adina Williams