Before viewing I/O Segment Details, ensure you set the value of the Oracle statistics_level parameter from TYPICAL to ALL.
Note: TYPICAL is the default STATISTICS_LEVEL setting recommended by Oracle. Setting the STATISTICS_LEVEL parameter to ALL instructs Oracle to collect additional information on timed OS statistics and plan execution statistics. This information is gathered (by default) every 5 seconds, and can add significantly to the target system's CPU usage and system load.
How to set the value of the Oracle statistics_level