Based on prior knowledge, we can assume that the age group of "Senior" corresponds to individuals who are typically aged 60 and above, while the age group of "Adult" corresponds to individuals below the age of 60.

To analyze the relationship between the feature RIDAGEYR and the target task of predicting age group, we can examine the distribution of RIDAGEYR values for each age group.

Here is the analysis of the relationship between the RIDAGEYR feature and the target task:

- RIDAGEYR values for the age group "Adult" (below 60):
   - Typical RIDAGEYR values for Adult: [20.0, 35.0, 45.0, 50.0, 55.0]
   - Other RIDAGEYR values for Adult: [25.0, 30.0, 40.0, 42.0, 58.0, 59.0, 36.0, 47.0, 51.0, 57.0]
   
- RIDAGEYR values for the age group "Senior" (60 and above):
   - Typical RIDAGEYR values for Senior: [60.0, 65.0, 70.0, 75.0, 80.0]
   - Other RIDAGEYR values for Senior: [62.0, 63.0, 68.0, 72.0, 77.0, 81.0, 85.0, 90.0, 65.0, 70.0, 76.0]

Based on this analysis, we can now create the dictionary in the required format:

```json
{
	"Adult": [20.0, 35.0, 45.0, 50.0, 55.0],
	"Senior": [60.0, 65.0, 70.0, 75.0, 80.0]
}
```