A hearing device comprising - a housing (211, 212) configured to be worn at an ear of a user; - a movement detector mechanically coupled to the housing (211, 212), the movement detector configured to provide movement data indicative of a movement of the housing; and - a processor communicatively coupled to the movement detector, the processor configured to identify, based on the movement data, a plurality of movement features (407 - 409, 507 - 510) in a sequence, the movement features representative of a movement activity carried out by the user, and to determine a temporal characteristic (311, 417 - 419, 513 - 518) of the sequence of movement features and/or to determine an amplitude characteristic (312, 407 - 409, 507 - 510) of the movement data associated with at least one of the movement features identified in the sequence; and to maintain a data record (309, 638, 639) representative of the temporal characteristic (311, 417 - 419, 513 - 518) and/or the amplitude characteristic (312, 407 - 409, 507 - 510) determined at a plurality of times; and to determine a deviation measure indicative of a deviation between the data record (309, 638, 639) and the temporal characteristic (311, 417 - 419, 513 - 518) and/or the amplitude characteristic (312, 407 - 409, 507 - 510) determined at a time later than said plurality of times; characterized in that the movement features are representative of a walking activity of the user and/or sequential manual tappings causing the movement of the housing, wherein the processor is further configured to control an operation of the hearing device depending on the deviation measure, wherein the operation comprises determining a parameter indicative of a change of a cognitive capability of the user depending on the deviation measure. - a housing (211, 212) configured to be worn at an ear of a user; - a movement detector mechanically coupled to the housing (211, 212), the movement detector configured to provide movement data indicative of a movement of the housing; and - a processor communicatively coupled to the movement detector, the processor configured to identify, based on the movement data, a plurality of movement features (407 - 409, 507 - 510) in a sequence, the movement features representative of a movement activity carried out by the user, and to determine a temporal characteristic (311, 417 - 419, 513 - 518) of the sequence of movement features and/or to determine an amplitude characteristic (312, 407 - 409, 507 - 510) of the movement data associated with at least one of the movement features identified in the sequence; and to maintain a data record (309, 638, 639) representative of the temporal characteristic (311, 417 - 419, 513 - 518) and/or the amplitude characteristic (312, 407 - 409, 507 - 510) determined at a plurality of times; and to determine a deviation measure indicative of a deviation between the data record (309, 638, 639) and the temporal characteristic (311, 417 - 419, 513 - 518) and/or the amplitude characteristic (312, 407 - 409, 507 - 510) determined at a time later than said plurality of times; characterized in that the movement features are representative of a walking activity of the user and/or sequential manual tappings causing the movement of the housing, wherein the processor is further configured to control an operation of the hearing device depending on the deviation measure, wherein the operation comprises determining a parameter indicative of a change of a cognitive capability of the user depending on the deviation measure. identify, based on the movement data, a plurality of movement features (407 - 409, 507 - 510) in a sequence, the movement features representative of a movement activity carried out by the user, and to determine a temporal characteristic (311, 417 - 419, 513 - 518) of the sequence of movement features and/or to determine an amplitude characteristic (312, 407 - 409, 507 - 510) of the movement data associated with at least one of the movement features identified in the sequence; and to maintain a data record (309, 638, 639) representative of the temporal characteristic (311, 417 - 419, 513 - 518) and/or the amplitude characteristic (312, 407 - 409, 507 - 510) determined at a plurality of times; and to determine a deviation measure indicative of a deviation between the data record (309, 638, 639) and the temporal characteristic (311, 417 - 419, 513 - 518) and/or the amplitude characteristic (312, 407 - 409, 507 - 510) determined at a time later than said plurality of times; characterized in that the movement features are representative of a walking activity of the user and/or sequential manual tappings causing the movement of the housing, wherein the processor is further configured to control an operation of the hearing device depending on the deviation measure, wherein the operation comprises determining a parameter indicative of a change of a cognitive capability of the user depending on the deviation measure.