Speech perception in noise (SPiN) is particularly critical during early development when infants and toddlers are acquiring language in environments that are often noisy, such as nurseries. Effective SPiN processing relies on coordinated neural networks supporting both top-down prediction and listening effort, as well as bottom-up auditory processing. Adult neuroimaging studies have identified involvement of several key brain regions in SPiN, including the left inferior frontal gyrus (IFG), the parietal lobe, sensorimotor areas, and temporal lobes. However, the mechanisms underlying SPiN in the immature infant brain remain unclear. Infants typically exhibit lower tolerance for background noise during language comprehension compared to adults, suggesting potential differences in neural processing strategies. To investigate this, we applied high-density diffuse optical tomography (HD-DOT) combined with Granger causality analysis to measure hemodynamic responses in 6- to 8-month-old infants exposed to audiovisual nursery rhymes under three conditions of speech clarity: clear (high clarity), and two degraded conditions at 8 dB and 4 dB signal-to-noise ratio. These conditions elicited distinct patterns of top-down versus bottom-up connectivity. Under the highest clarity condition, we observed strong top-down language prediction signals from the left IFG to the left inferior parietal lobule (IPL), which diminished as speech clarity decreased. Conversely, degraded speech conditions elicited enhanced connectivity between frontal and sensorimotor regions, consistent with increased listening effort. Right hemisphere engagement shifted between bottom-up and top-down connectivity patterns depending on the difficulty of the listening condition. These findings provide preliminary evidence that Granger causality analysis combined with HD-DOT is a viable method to investigate speech in noise processing in pre-verbal infants. Understanding these early neural mechanisms may inform interventions for infants at risk of speech and language difficulties in challenging acoustic environments.